Mindfulness-based interventions in schools—a systematic review and meta-analysis

Abstract

Mindfulness programs for schools are popular. We systematically reviewed the evidence regarding the effects of school-based mindfulness interventions on psychological outcomes, using a comprehensive search strategy designed to locate both published and unpublished studies. Systematic searches in 12 databases were performed in August 2012. Further studies were identified via hand search and contact with experts. Two reviewers independently extracted the data, also selecting information about intervention programs (elements, structure etc.), feasibility, and acceptance. Twenty-four studies were identified, of which 13 were published. Nineteen studies used a controlled design. In total, 1348 students were instructed in mindfulness, with 876 serving as controls, ranging from grade 1 to 12. Overall effect sizes were Hedge's g = 0.40 between groups and g = 0.41 within groups (p < 0.0001). Between group effect sizes for domains were: cognitive performance g = 0.80, stress g = 0.39, resilience g = 0.36, (all p < 0.05), emotional problems g = 0.19 third person ratings g = 0.25 (both n.s.). All in all, mindfulness-based interventions in children and youths hold promise, particularly in relation to improving cognitive performance and resilience to stress. However, the diversity of study samples, variety in implementation and exercises, and wide range of instruments used require a careful and differentiated examination of data. There is great heterogeneity, many studies are underpowered, and measuring effects of Mindfulness in this setting is challenging. The field is nascent and recommendations will be provided as to how interventions and research of these interventions may proceed.

Full text

ORIGINAL RESEARCH ARTICLE
published: 30 June 2014
doi: 10.3389/fpsyg.2014.00603
Mindfulness-based interventions in schools—a systematic
review and meta-analysis
Charlotte Zenner , Solveig Herrnleben-Kurz and Harald Walach*
Institute for Transcultural Health Studies, European University Viadrina, Frankfurt Oder, Germany
Edited by:
Jesus De La Fuente, University of
Almería, Spain
Reviewed by:
Kathy Ellen Green, University of
Denver, USA
Olusola Olalekan Adesope,
Washington State University, USA
*Correspondence:
Harald Walach, Institute for
Transcultural Health Studies,
European University Viadrina,
Grosse Scharrnstrasse 59,
15207 Frankfurt Oder, Germany
e-mail: walach@europa-uni.de
Mindfulness programs for schools are popular. We systematically reviewed the evidence
regarding the effects of school-based mindfulness interventions on psychological
outcomes, using a comprehensive search strategy designed to locate both published and
unpublished studies. Systematic searches in 12 databases were performed in August
2012. Further studies were identified via hand search and contact with experts. Two
reviewers independently extracted the data, also selecting information about intervention
programs (elements, structure etc.), feasibility, and acceptance. Twenty-four studies were
identified, of which 13 were published. Nineteen studies used a controlled design. In total,
1348 students were instructed in mindfulness, with 876 serving as controls, ranging from
grade 1 to 12. Overall effect sizes were Hedge’s g=0.40 between groups and g=0.41
within groups (p<0.0001). Between group effect sizes for domains were: cognitive
performance g=0.80, stress g=0.39, resilience g=0.36, (all p<0.05), emotional
problems g=0.19 third person ratings g=0.25 (both n.s.). All in all, mindfulness-based
interventions in children and youths hold promise, particularly in relation to improving
cognitive performance and resilience to stress. However, the diversity of study samples,
variety in implementation and exercises, and wide range of instruments used require a
careful and differentiated examination of data. There is great heterogeneity, many studies
are underpowered, and measuring effects of Mindfulness in this setting is challenging.
The field is nascent and recommendations will be provided as to how interventions and
research of these interventions may proceed.
Keywords: mindfulness, children, meta-analysis, systematic review, stress, school-age, resilience
INTRODUCTION AND BACKGROUND
The application of Mindfulness-Based Interventions (MBIs) has
become increasingly popular in the last few years, both in research
and practice. Mindfulness can be defined as the psychological
capacity to stay willfully present with one’s experiences, with a
non-judgemental or accepting attitude, engendering a warm and
friendly openness and curiosity (Kabat-Zinn, 2005).
Originally derived from eastern traditions and Buddhist psy-
chology, mindfulness can be cultivated by various techniques
(Bankart, 2003; Wallace and Shapiro, 2006). Formally, it is trained
by meditation practices such as sitting meditation, or physical
movement such as yoga or tai chi. These techniques help steady
the mind and train its attentional capacity, while also increas-
ing its breadth of focus. Practitioners are instructed to focus their
attention on the present moment using an “anchor,” for instance,
the breath. When the mind drifts away, the focus is gently brought
back to the present moment experience. The practitioner tries
to simply observe his or her experience of the present moment
without judging or modifying it.
Roughly 30 years ago, Jon Kabat-Zinn introduced mindful-
ness as a resource into clinical research and practice through
the Mindfulness-Based Stress Reduction Program (MBSR). The
MBSR program consists of 8 weekly sessions of 2½ h, and
a day of mindfulness. Mindfulness is practiced formally in
sitting meditation, by simple yoga movements, and in the body-
scan, which is a gradual sweeping of attention through the
body. Mindfulness is also cultivated in daily activities such as
eating, and by using it as a resource in emotionally challeng-
ing situations or in dealing with physical pain. The recom-
mended daily home practice lasts approximately 45min, and
includes formal and informal exercises. Moreover, the program
includes psycho-education, and attitudes such as not judging, a
beginner’s mind, trust, non-striving, acceptance, letting go, and
patience are encompassed (Kabat-Zinn, 1982, 1990, 2003). The
MBSR program became the parent to several variations, such as
Mindfulness-Based Cognitive Therapy (MBCT; Segal et al., 2002),
initially developed for preventing relapse of depression. In other
cognitive-behavioral therapies, such as acceptance and commit-
ment therapy, (ACT; Hayes et al., 1999) and dialectical behavior
therapy (DBT; Linehan, 1993), the emphasis of treatment lies on
acceptance as well as on change.
In several reviews and meta-analyses, MBIs proved to be effec-
tive in a wide range of stress related and clinical problems and dis-
orders for various disease groups (Grossman et al., 2004; Fjorback
et al., 2011; Piet and Hougaard, 2011; Piet et al., 2012). In
addition, an interesting aspect of MBIs is their potential preven-
tive and health promoting capacity in non-clinical populations:
reducing stress, increasing well-being and strengthening immune
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Zenner et al. Mindfulness-based interventions in schools
functions (Davidson et al., 2003; Chiesa and Serretti, 2009; Eberth
and Sedlmeier, 2012); promoting personal development such as
self-compassion, empathy and perspective taking (Shapiro et al.,
1998, 2007; Birnie et al., 2010); increasing attentional capacity
(Jha et al., 2007; Tang et al., 2007)andthetemporalwindowof
attention (Sauer et al., 2012).
One potential mechanism could be through decreasing the
tendency to avoid unwanted experiences, thus generally improv-
ing positive affect (Sauer et al., 2011a,b). Mindfulness seems to
be the opposite of mind-wandering (Smallwood and Schooler,
2006). Mind-wandering has been linked to the activity of the
default-mode network (DMN), i.e., those areas of the brain that
become active when the cognitive system remains idle (Raichle
et al., 2001). Interestingly, experienced Zen meditators show
reduced baseline activity of the DMN (Pagnoni et al., 2008).
Since a higher activity of the DMN is related to increased neg-
ative affect and to the rate of mistakes in attentional and other
tasks (Smallwood et al., 2011), it seems natural that reducing
mind-wandering and improving attentional capacities could be
beneficial in many respects, and might be one of the generic
mechanisms through which mindfulness-based approaches work
(Carmody, 2009).
Given the diverse usefulness and beneficial record of MBIs for
adults, researchers and clinicians are striving to develop adap-
tations for children and youths. Research is in its infancy, but
initial reviews suggest that MBIs are feasible with children and
adolescents and seem to be beneficial in both clinical and non-
clinical samples (Black et al., 2009; Burke, 2009). They have been
successfully applied to adolescents with attention deficit hyper-
activity disorder (ADHD) symptoms (Van der Oord et al., 2012;
Weijer-Bergsma et al., 2012), and to adolescents with a vari-
ety of externalizing disorders (Bögels et al., 2008). MBIs lead
to a reduction in symptoms of depression in minority children
(Liehr and Diaz, 2010) and to a reduction in anxiety and increase
of social skills in students with learning disorders (Beauchemin
et al., 2008). In a study of “at-risk” and HIV-positive youth,
decreases in hostility and general and emotional discomfort have
been reported, while qualitative data indicated improvements in
academic performance, interpersonal relations, stress-reduction,
and physical health (Sibinga et al., 2011). Also, first conceptual
frameworks have been created as to why MBI’s are beneficial for
children and youth and how mechanisms might work (Mind and
Life Education Research Network (MLERN), 2012; Zelazo and
Lyons, 2012).
School appears to be an appropriate setting for such interven-
tions, since children spend a lot of time there and interventions
can be brought directly to groups of children in areas of need
as part of a preventive approach at little cost (Weare and Nind,
2011). Mindfulness can be understood as the foundation and
basic pre-condition for education. Children need to learn to
stop their mind wandering and regulate attention and emo-
tions, to deal with feelings of frustration, and to self-motivate.
Mindfulness practice enhances the very qualities and goals of
education in the 21st century. These qualities include not only
attentional and emotional self-regulation, but also prosocial dis-
positions such as empathy and compassion, self-representations,
ethical sensitivity, creativity, and problem solving skills. They
enable children to deal with future challenges of the rapidly
changing world, ideally becoming smart, caring, and committed
citizens (Shapiro et al., 2008; Mind and Life Education Research
Network (MLERN), 2012).
Concurrently, reports of increasing clinical problems in chil-
dren, stress-related problems and problems related to social pres-
sure in and outside school are worrying. Children and youth
frequently experience stress in school (Currie et al., 2002; Lohaus
and Ball, 2006; Card and Hodges, 2008), which has an impact
on the brain structures involved in cognition and mental-health
(Lupien et al., 2009). Serious mental disorders are also widespread
among children. It has been reported that 21% of the 13 to 18 year
olds in the US are currently suffering, or have at some point dur-
ing their life suffered, from a severe mental disorder (Merikangas
et al., 2010), with ADHD, behavioral or conduct problems, anx-
iety, and depression being the most prevalent current diagnoses
(US Department of Health and Human Services, and Centers for
Disease Control and Prevention, 2013).
Formal education should always consider the mental health
and balance of children. A growing body of research shows that
“academic achievement, social and emotional competence and
physical and mental health are fundamentally and multiply inter-
related. The best and most efficient way to foster any of those is
to foster all of them” (Diamond, 2010, p. 789). Schools are there-
fore confronted with the task of not only being institutions for
formal education, but also a place that provides tools for prevent-
ing disorders and fostering personal development and well-being
in children. These needs have driven educators, teachers, and psy-
chologists to seek methods to improve school-based learning and
the social experience connected with it. MBIs in schools are seen
as an approach to tackle these challenges, because prevention
and education can be provided simultaneously, addressing a wide
range of needs and unfulfilled potentials of students.
As a result, various mindfulness programs for schools have
been developed and applied within the past few years (see
Meiklejohn et al., 2012 for an overview). Several research insti-
tutes and associations, such as the Garrison Institute, are initi-
ating workshops and conferences on Mindfulness in Education
on a regular basis. Within mailing lists administrated by the
Mindfulness in Education Network (www.mindfuled.org) or the
Association of Mindfulness in Education (www.mindfuleducation.
org), clinicians, educators, and researchers from all over the world
share ideas, material and experiences of mindfulness in schools.
The increasing amount of meetings, books, and newspaper arti-
cles indicate that the integration of mindfulness into education is
received with great interest and is seen as a potentially plausible,
cost-effective, and promising approach.
ThenumberofstudiesevaluatingMBI’sinschoolsettingsis
also growing. However, others point out that, to date, enthusi-
asm about the integration of MBI’s in schools surpasses evidence
(Greenberg and Harris, 2011). The diversity of programmes and
outcome measures combined with the pilot-character of most
studies make it difficult to get a general impression of effective-
ness, and directions of further research cannot be easily derived.
Presenting a narrative review on the literature, Meiklejohn et al.
(2012) made a good start summarizing the research published to
date, but a quantitative synthesis exclusively integrating studies
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Zenner et al. Mindfulness-based interventions in schools
on MBI’s in school context is still lacking. Specifically, it would be
helpful to know if there are specific domains in which MBI’s are
particularly beneficial. At this point the inclusion of unpublished
literature, such as doctoral theses, would enrich the discussion,
as these often contain supplementary information that could
be valuable and could introduce new approaches to this spe-
cific research field, such as, for example, the choice of measures.
Also, little is known about the feasibility of integrating MBI’s
into school-routine, for example, the acceptability of different
programme elements.
To help progress this field of research, we decided to carry out
a meta-analytic review. Aiming to give a complete insight into the
actual state of the art, we adopted a very open and comprehen-
sive stance by locating as many studies as possible, both published
and unpublished, and by including all relevant material. First, we
addressed the types of mindfulness interventions that have been
applied and the measures used in order to provide a transparent
overview of the field. Second, we explored how MBI’s work in
a school setting: collecting findings on feasibility and acceptabil-
ity. With a view to provide recommendations for future research,
third, we ascertained the quality of the existing trials and iden-
tified possible methodological challenges. Fourth, we carried out
a quantitative synthesis in order to ascertain whether effect sizes
warrant pursuing this line of research further. By also deriving
domain-specific effect sizes, we aimed to clarify the diversity of
outcome measures and to address the issue of which domains
might be most beneficial for school children.
Since the work was exploratory, it was intended to give orien-
tation and develop further hypotheses rather than to test them. In
the following, we present a systematic review of the literature and
a meta-analysis of the available information.
METHODS
SEARCH STRATEGY
A comprehensive search strategy was chosen in order to
locate both published and unpublished studies. In August
2012 systematic searches were performed in 12 databases
and catalogs including Web of Knowledge, SciVerse Hub,
PsychARTICLES, PSYNDEX, Psychology and Behavioral Sciences
Collection, ERIC, FIS, The DART-Europe E-Theses Portal, PDQT
Open, DissOnline, Openthesis, and UMI Dissertation Express.
Mindfulness_ was used as the key word, combined with School_,
Classroom_, or Education_, where appropriate. Studies were
searched from the first year the database was available and no
language restrictions were applied.
After removal of duplicates and screening abstracts of the
remaining studies, full-text articles of relevant studies were
retrieved for examination. The reference lists of the selected
articles were inspected and authors of relevant studies were
contacted. Emails were sent to the mailing list of Mindfulness
in Education Network and the Association of Mindfulness in
Education in October 2012. All volumes of the Mindfulness
Research Monthly Newsletter and Mindfulness Journal were
screened up to and including October 2012.
The first two authors independently extracted the data
from the original reports in order to decide on inclusion.
Disagreements were solved by discussion.
INCLUSION CRITERIA
Studies were selected if the following criteria were met:
(1) Interventions were mindfulness-based.
(2) Implementation took place in a school-setting.
(3) Participants were pupils or students from grade 1 to 12.
(4) Outcomes were quantitative data, referring to psychological
aspects.
We sought interventions based on the concept of mindfulness,
with classical mindfulness practices such as mindful breathing
or the body scan as core elements. Combinations with other
methods, such as massage, imaginary journey, or games, were
accepted as long as their implementation was aimed at cul-
tivating mindfulness, making it easily accessible for the tar-
get age-group and setting. Approaches combining mindfulness
and other established techniques such as Autogenic Training or
Progressive Muscle Relaxation were excluded, because outcomes
cannot clearly be attributed to mindfulness. For the same reason
evaluations of trainings mainly based on concentrative medita-
tion, such as Transcendental Meditation, were also excluded. No
further methodological exclusion criteria were applied.
DATA EXTRACTION
Data on methodology and outcomes of included studies were
extracted and coded by the first author and checked by the sec-
ond author. These data covered information on schools and
participants, sample size and study design, applied measures,
type of statistical analysis and major findings reported, as well
as data necessary for calculating effect sizes. Relevant informa-
tion concerning interventions and feasibility was extracted by the
second author and checked by the first author. This information
included setting, structure, and elements of intervention and var-
ious aspects of feasibility (e.g., acceptability, fidelity, attrition). In
cases where important information was missing, study authors
were contacted.
STATISTICAL METHODS
The weighted mean effect size (ES) gwas chosen as a statistic for
final analysis. Hedges’s gis a variation of Cohen’s d(Cohen, 1988),
standardizing the mean difference by a pooled standard deviation
using n-1 for each sample (Hedges and Olkin, 1985).
ghedges=M1−M2
spooled
with spooled =(n1−1)s2
1+(n2−1)s2
2
n1+n2−2(1)
ESs were then multiplied with c(m), a correction factor to correct
potential bias due to small sample sizes.
c(m)=1−3
4m−1(2)
where mrefers to degrees of freedom used to estimated spooled
(Hedges, 1981). Hedges’s gcan be interpreted according to
Cohen’s ES conventions (1988) as small (0.2), medium (0.5), and
large (0.8).
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Zenner et al. Mindfulness-based interventions in schools
Within-group ES were calculated for all relevant measures in
every study. For controlled trials ES of baseline equivalence and
differences in change scores were also derived.
In several cases means and standard deviations were not
reported. If statistics like partial eta-squared (interpreted as r2),
t-orF-values were given, gcould be derived according to spe-
cific formulas. In other cases, all essential data were missing and
authors did not provide them after being contacted. In order to
prevent bias due to missing data, ES were estimated in alterna-
tive ways (marked with a #). Lacking means, for example, could
be derived from graphs (8, 14). Missing SDs for within-group
differences were estimated by deriving standard error of change
score differences (8), or were derived from SD of within-group
differences, assuming that population variance at time 1 and 2
was equal (18). In another study, standard deviations of the norm
sample were used for ES calculation (22). If no information was
neither reported nor could be extracted, results were suggested
to be insignificant and thus ES were estimated as 0 (Rosenthal,
1995). This was done for study no. 8, 12, 18, and 22 (see
Tab l e 1).
Two kinds of overall ESs were estimated. First, a within-group
effect size was derived, based on the average of pre-post changes of
intervention group in every study. Second, a controlled between-
group effect size was calculated for all controlled trials. It was
based on average change score differences between interven-
tion group and control. A change score comparison was chosen
instead of a simple post-test comparison, because baseline equiv-
alence could not be assumed for all studies, and this might bias
the estimation of intervention effects.
Standard errors of within group and controlled effect sizes
were calculated according to the following formulas:
SEwithin group =1
n+g2
2(n−1) and
SEcontrolled =n1+n2
n1n2
+g2
2(n1+n2)(3)
Initially, we grouped ES into four domains which had been shown
to be affected by mindfulness practice in adults according to
measurement method and construct: perceived stress and cop-
ing (S), factors of resilience (R), and emotional problems (E)
were measured via self-report scales. A domain of cognitive per-
formance (C) was measured by performance tests. Subsequently,
given that a lot of studies used questionnaires for parents and
teachers addressing various domains, we created a fifth domain
containing third person ratings (T) exclusively. Independence of
results was ensured for all analysis. Where a study contributed
several ES to the same domain, ES were averaged.
Reliability of measures could not be used to adjust effect-sizes,
as authors did not consistently report reliability and the measures
that were reported were not compatible with each other.
The inverse variance random-effects model (DerSimonian and
Laird, 1986) was chosen to carry out quantitative synthesis. This
model incorporates an assumption that the population parame-
ters vary from study to study. As a consequence, variation in effect
sizes are not only caused by sampling error, but also occur due
to differences between hyperparameter and population parameter
values. Thus, results can be generalized beyond the included stud-
ies. The between-study variance tau-squared (τ2) is the estimated
standard deviation of underlying effects across studies.
Heterogeneity between studies was assessed via the Qand the
I2statistic. The Q-test determines the probability of sampling
errors being the only cause for variance. Under the hypothesis
of homogeneity among effect sizes, the Qstatistic follows the
chi-square distribution. As a result, significant Q-values can be
considered as evidence for heterogeneity because variance is also
due to differences between effect sizes. The I2index describes the
percentage of the variability in effect estimates that is caused by
heterogeneity. I2of around 25, 50, and 75% would be interpreted
as low, medium, and high heterogeneity. To identify publication
bias a funnel plot was used. A funnel plot is a scattergram where
the ES is plotted at the horizontal axis and the study size is plot-
ted on the vertical axis. With no availability bias, one should
see a funnel turned upside down. In case of bias, when smaller
studies without significant effects were not available, the scat-
tergram should deviate noticeably from the symmetrical funnel
shape. Additionally we used the fail-safe Nas a rough measure
of the robustness of our analysis against availability bias. The
fail-safe number (kfs) estimates the number of unavailable null
result studies that would be required to render the overall plevel
of the meta-analysis insignificant. If the fail-safe number is large
(largerthan5k+10), essential influence of bias on mean effects
of meta-analysis are unlikely (Rosenthal, 1991).
FEASIBILITY
When a new intervention has just been implemented, informa-
tion on feasibility of the process is a rich source for improvement,
refinement, and adaptation of the intervention at later stages. The
term feasibility here is understood as assessing the applicability
of the different programs, their strengths, and weaknesses. For
this analysis of the data we assumed two different areas of focus
(Bowen et al., 2010): (1). Acceptability: to what extent the program
is judged as suitable, satisfying, or attractive to program deliv-
erers (teachers) and recipients (students). (2). Implementation:
to what extent the program is successfully delivered to intended
participants in the context of daily school-routine.
RESULTS
TRIAL FLOW
In Figure 1, the study selection process is visualized in a PRISMA
flow diagram (Moher et al., 2009). The initial search provided 207
possibly relevant records after duplicates were removed. One hun-
dred and sixty-five records were excluded after screening, mostly
because they were reports or conceptual papers rather than
experimental or scientific studies. Further screening of 42 full
manuscripts against inclusion criteria identified 24 studies. The
most prevalent reasons for exclusion at this stage were that the
intervention could not clearly be defined as solely mindfulness-
based (K=9), but was combined with relaxation techniques such
as Progressive Muscle Relaxation, visualization, or bio-feedback.
Further, three studies were excluded because the intervention was
implemented in a setting other than regular school life, such as
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Zenner et al. Mindfulness-based interventions in schools
Table 1 | Empirical studies on MBI’s in a school-setting.
Study NAge range,
mean (SD),
grade and
gender
School/
participant
description
(country)
Study design Measures and
domain
gHedges
Baseline
equivalence
gHedges
Within-
group
gHedge
Differences
in change
scores
Reported findings according to authors
RANDOMIZED CONTROLLED TRIALS
1. Desmond and
Ha nich, 2 010
40 11–12,
6th grade
41% female
Urban, public
middle school,
low income
(USA)
M-group (n=15)
vs. C (n=25)
BRIEF (teacher) T0.26 0.04 0.31 MANOVAs: No sig. time by group interaction (all ps
>0.05). Multiple regression analysis: Sig. interaction
between pre-test score and group membership for
predicting differences in one of eight subscales,
indicating that M-group showed greater
improvement in ability to shift (p<0.05). In general,
M-group maintained or improved executive function
skills, while C shows a decline.
2. Flook et al., 2010 64 7–9
8.23 (0.66)
2nd +3rd grade
55% female
On-campus
university
elementary
school, diverse
ethical
backgrounds
(USA)
M-group (n=32)
vs. C (n=32)
BRIEF (teacher)
BRIEF (parent)
T
T
0.31
0.27
0.20
0.39
0.08
0.12
MANCOVAs with post-test scores as outcome
variables: No sig. group main effect, indicating no
group differences for pre- to post-test (p<0.05). Sig.
interaction between baseline levels and group in
teacher report (p=0.005) as well as in parent report
(p=0.020). In M-group, children with poorer initial
executive function showed greater improvement at
Time 2 compared to C.
3. Franco Justo, 2009 60 15–18
17.3
1st +2nd year
high school
72% female
3 public
secondary
schools
(Spain)
M-group (n=30)
vs. waitlist c
(n=30), follow-up
after 3 months
TTCT (verbal)
-Fluency
-Flexibility
-Originality
C
−0.11
0.05
−0.05
1. 5 0
1. 5 3
1. 6 1
1. 4 8
1. 8 7
1. 6 7
Independent and dependent t-Tests: Sig.
improvement from pre- to post-test in M-group in all
subscales (Fluency, Flexibility, Originality; all ps<
0.01) and no improvement in C (all ps>0.05). At
post-test M-group shows significantly higher scores
in all subscales compared to C (all ps<0.01). Effects
sustained at follow up compared to pre-test (all ps=
0.001), but not compared to post-test (all ps>0.05).
4. Franco Justo et al.,
2011a
61 16–18
16.75 (0.83)
1st year high
school
48% female
3 compulsory
secondary
schools, public
(Spain)
M-group (n=31)
vs. waitlist c
(n=30)
Schools were
allocated at
random
Grades
Self-concept
STAI
C
R
E
−0.27
0.59
0.35
1. 5 2
1. 5 5
0.62
1. 4 3
1. 8 4
0.11
Dependent and independent t-Tests: Sig.
improvement from pre- to post-test in M-group in all
measures (all ps=0.001) and no improvement in C
(all ps>0.05). Sig. difference between groups in
post-tests (all ps>0.01). Detailed analysis: students
with middle range academic performance show the
most improvement in Grades (Cohen’s d=3.05),
Students with low self-concept show most
improvement in self-concept (d=5.12), students
with high state anxiety benefited the most on state
anxiety (d=1.95) and students with medium trait
anxiety benefited the most on trait anxiety
(d=1.44).
(Continued)
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Zenner et al. Mindfulness-based interventions in schools
Table 1 | Continued
Study NAge range,
mean (SD),
grade and
gender
School/
participant
description
(country)
Study design Measures and
domain
gHedges
Baseline
equivalence
gHedges
Within-
group
gHedge
Differences
in change
scores
Reported findings according to authors
5. Franco Justo et al.,
2011b
84 16–19
17.06 (2.44)
1st +2nd year
high school
72% female
Various
compulsory
secondary
schools
(Spain)
M-group (n=42)
vs. waitlist
C(n=42)
AURE R−0.06 1.26 1.29 Dependent and independent t-Tests: Sig.
improvement from pre- to post-test in M-group for all
3 subfactors (1. Approaching and Coping with a Task
2. Self-Concept and Self-Esteem 3. Empathy and
Social Relations; all ps<0.05) and no improvement
in C (all ps>0.05). Sig. difference between groups
in post-tests in the first 2 subfactors (ps<0.001),
but not in the third (p=0.16).
6. Ma i, 2010 12 13–17
14.4 ( Mdn =
14.0),
9th grade,
25% female
Urban high
school, low socio
economic status,
low performing
(USA)
M-group (n=7)
vs. waitlist
C(n=5), follow-up
after 6 weeks
DERS
BRIC (teacher)
Grades
School
attendance
E
T
C
–
0.57
−0.12
−0.55
−0.05
−0.06
−0.10
0.02
0.29
−0.60
−0.10
0.30
0.10
ANOVAs (repeated measures): No sig. findings were
found (all ps>0.05).
7. Mendelson et al.,
2010
97 10.15 (0.7),
4th +5th grade
61% female
4 urban public
elementary
schools, low
income
neighborhood
with high levels
of violence
(USA)
2 M-groups
(n=42–47) vs. 2
waitlist
C(n=40–43)
4 schools were
allocated at
random
PAN AS
SMFQ—C
PIML
Involuntary
Engagement
(RSQ)
R
E
R
S
−0,14
0.9
−0.21
0
0.17
0.14
−0.02
0.41
0.23
0.02
0.09
0.90
Multiple regressions: M-group demonstrated sig.
improvements on the overall scale of Involuntary
Engagement compared to C (p<0.001). Sig.
differences were found on three of the five subcales
(Rumination, Emotional Arousal, Intrusive Thoughts:
p<0.05) and a trend for Impulsive Action and
Physiologic Arousal (boths ps<0.07). No other sig.
results were found. However, depressive symptoms
and negative effect displayed a pattern consistent
with predictions.
8. Napoli et al., 2005 194 1st-3rd grade 2 elementary
schools
(USA)
M-group (n=97)
vs. C (n=97)
ACTeRS (teacher)
TAS
Selective
Attention
(TEA-Ch)
Sustained
Attention
(TEA-Ch)
T
E
C
C
#
#
#
#
0.20#
0.38#
0.48#
0#
0.24
0.39
0.60
0.13
T-Tests for change scores between groups: Sig.
improvement for M-group on attention and social
skills subcale of ACTeRS (both ps=0.001).Sig.
reduction of Test Anxiety in M-group (p=0.007).
Sig. improvement of M-group on selective attention
(p<0.001) but not on sustained attention subscale
(p=0.350).
9. Pote k, 2 012 30 14–17
15 (0.98)
9th-12th grade
48% female
2 high schools in
an urban or rural
setting, diverse
range of
socioeconomic
status (USA)
M-group (n=16)
vs. waitlist
C(n=14)
MASC
DERS
PSS
E
E
S
0.01
0.32
0.25
1. 12
0.27
0.49
0.85
0.33
0.42
Repeated-measures ANOVAs: Sig. interaction
between time and group on MASC scores
(p<0.0001), indicating that the anxiety level of
M-group decreased more compared to C. No sig.
interaction effect on DERS and PSS scores (boths
ps=0.14).
(Continued)
Frontiers in Psychology | Educational Psychology June 2014 | Volume 5 | Article 603 |6

Zenner et al. Mindfulness-based interventions in schools
Table 1 | Continued
Study NAge range,
mean (SD),
grade and
gender
School/
participant
description
(country)
Study design Measures and
domain
gHedges
Baseline
equivalence
gHedges
Within-
group
gHedge
Differences
in change
scores
Reported findings according to authors
10. White, 2012 155 8– 11
9.9 (0.72)
4th +5th grade
100% female
Public schools,
85% reported
having no family
stress or health
problems,
majority of parents
went to college
(USA)
M-group (n=70)
vs. waitlist
C(n=85)
FBS
SCSI
Global Self-worth
Scale (SPPC)
S
S
R
0.16
−0.05
0
−0.17
0.05
0.17
−0.11
0.16
−0.18
Repeated-measures ANOVAs: Sig. time by group
interaction on the SCSI subscale frequency of coping
(p<0.04), suggesting that M-group is coping more
frequently after intervention. No sig. interaction for
Global self-worth (p=0.57) and an approached
significance for FBS (p=0.06), indicating increasing
stress levels in M-group after intervention compared
to C. Further analysis revealed that this was due to a
sig. interaction for the stress appraisal subscale of
FBS (p=0.005). Compared to C, M-group was more
likely to increase their appraisal of stress at post-test.
QUASI-RANDOMIZED CONTROLLED TRIALS
11. Broderick and
Metz, 2009
122 16– 19
M-group:
Seniors 17.43
(0.53)
C: Juniors 16.41
(0.85)
100% female
Suburban,
private catholic
high school for
female
(USA)
M-group (seniors, n
=105, age:
M=17.43)
vs.
C (juniors, n=17,
age: M=16.41)
PAN AS
Calm/relaxed/
self-accepting
scale
DERS
Reflective
pondering (RRS)
Moody pondering
(RRS)
SICBC
R
R
E
E
E
E
−0.21
0.03
0.13
0.18
0.09
0.10
0.24
0.33
0.20
0.01
0.19
0.24
0.55
0.55
0.18
0.08
0.22
0.13
T-Tests for change scores between groups: M-group
demonstrated sig. reduction in neg. affect and sig.
increase on the calm/relaxed/self-accepting scale
(both ps<0.05). No other measures showed sig.
differences in gain scores (p>0.05).
Dependet t-tests: M-group showed sig. decline in
neg. emotions and somatic complaints, sig. increase
in the calm/relaxed/self-accepting scale and emotion
regulation (all ps<0.01). No sig. findings on the RRS
factors (p>0.05).
12. Corbett, 2011 107 8– 11
9.94 (0.76)
4th +5th grade
47% female
Elementary
school located at
university
campus,
(Florida, USA)
M-group (n=63)
vs. C (n=44),
cortisol measures:
M-group (n=12)
vs. C (n=13)
State
Anxiety (STAIC)
TAS-C
PANAS-C
CCTT
Pop quiz
Salivary cortisol
E
E
R
C
–
–
0.70
0.52
0.37
−0.50
−0.37
−0.74
#
0.11
0.07
0.84
1. 0 6
0.02
0#
−0.63
−0.43
1. 18
−0.44
0.14
ANCOVAs with pretest scores as covariates: No sig.
differences between M-group and C in test anxiety,
cortisol release, positive, and negative affect after
the Mindfulness training (all ps>0.05).
ANOVA on STAIC difference scores showed no sig.
difference between groups in level of reported state
anxiety (p>0.05). ANOVA on pop quiz scores
demonstrated no sig. difference between groups
(p>0.05).
13. Frenkel et al.,
in press
47 13–15
14.59 (0.54)
9th grade
46% female
Private secondary
school
(Germany)
M-group (n=24)
vs. waitlist C
(n=23)
Classes had been
assigned randomly
to conditions,
follow up after 6
weeks.
Test d 2
Unnoticed Mind
Wandering
Mind Wandering
noticed by others
Self-noticed Mind
Wandering
PSQ
Kiddo-KINDL-R
PAN AS
KINDL (parents)
C
C
C
C
S
R
R
T
0.04
0.20
−0.86
0.11
0.42
−0.23
0.03
0.38
1. 4 8
0.13
0.84
0.35
0.22
0.06
0.11
0.35
−0.06
0.15
1. 2 6
0.38
−0.12
−0.11
−0.18
−0.35
MANOVAs: marginally sig. improvement in
combined parents ratings (p=0.071) and measures
of cognitive performance (p=0.067).
ANOVAs: M-group demonstrated sig. decrease in
mind wandering noticed by others (p<0. 05) which
sustained in f –up (p<0.10). Subjects in M-group
were more likely not to notice their Mind Wandering
(self-noticed Mind Wandering p<0.10).
(Continued)
www.frontiersin.org June 2014 | Volume 5 | Article 603 |7

Zenner et al. Mindfulness-based interventions in schools
Table 1 | Continued
Study NAge range,
mean (SD),
grade and
gender
School/
participant
description
(country)
Study design Measures and
domain
gHedges
Baseline
equivalence
gHedges
Within-
group
gHedge
Differences
in change
scores
Reported findings according to authors
14. Hennelly, 2011 99 11–17
7th-12th grade
50% female
3typical,
mixed-gender
state secondary
schools (UK)
M-group (n=53)
vs. C (n=46),
follow-up after 6
months
WEMWBS
ERS
R
R
−0.11
0.53#
0.19
0.04#
0.41
0.08#
ANOVAs and pairwise comparisons by age, gender
and group: Sig. effects on well-being due to
decreasing scores of C, while participants scores
remained steady (p<0.05). In Ego-Resilience only
the oldest students of M-group (12 Grade) reported
sig. improvement (p<0.05). Female participants
ego-resilience increased compared to female
controls whereas male participants ego-resilience
reduced. At post-test, female participants scored sig.
higher on ERS than male participants (p<0.01) .
Compared to post-test, M-group showed a further
increase of well-being and a slight decrease of
ego-resilience at follow up.
15. Huppert and
Johnson, 2010
134 14– 15
100% male
2 independent,
fee-paying boys
schools, 5%
ethnic minorities
(UK)
M-group (n=78)
vs. C (n=56)
ERS
WEMWBS
R
R
−0.08
−0.09
0
0.26
0
0.34
Multiple regressions: no sig. overall differences
between M-group and C for resilience (p<0.05).
Condition was found to contribute marginally
significantly to change in well-being (p<0.01). Sig.
improvement of well-being related to the degree of
individual practice (p<0.05).
16. Metz et al., 2013 216 16,45 (0.95)
10th-12th grade
36% female
2 high schools
in a suburban
district (USA)
M-school (n=129)
vs. C—school
(n=87)
DERS
Psychosomatic
complaints
ASRES
Stress level Item
E
E
R
S
−0.11
0.03
−0.16
0.19
0.42
0.37
0.56
0.43
0.26
0.20
0.48
0.40
MANOVA on mean gain scores: Sig. difference
between groups (p=0.003) and approximately 12%
of multivariate variance of the dependent variable is
associated/can be explained by with the group factor.
ANOVAs: compared to C, M-group demonstrated
improvement in emotion regulation (p=0.021),
self-regulation efficacy (p=0.001) and a lager
reduction in psychosomatic complaints (p=0.043).
Sig. effect for several subscales of DERS and
psychosomatic items (all ps<0.05). M-group
reported 10% decrease in amount of stress,
whereas C stated no change (p=0.005).
17. Kohls and Sauer,
unpublished raw data
87 9th–12th
5th grade
Public secondary
school
(Germany)
M-group
(n=29–31) vs. C
(reading training:
n=24–26; passive:
n=22–30)
Attention test
KINDL
Vulnerability
(SSKJ)
Stress
symptoms (SSKJ)
Emotion-
Regulation Items
(SSKJ)
C
R
S
S
S
−0.34
−0.19
−0.36
−0.32
0.08
0.34
−0.02
0.07
−0.33
0.12
0.27
0.47
−0.03
0.02
0.25
Analysis of Effect sizes: M-Group demonstrated
improvement in Attention compared to C. Well-being
scores in M-group remained stable, whereas scores
in C were decreasing. No difference between groups
in vulnerability to stress and physical symptoms. In
psychological symptoms, M-group proved the
smallest increase. Compared to C, M-group showed
strongest improvement in emotion regulation in
response to stress.
(Continued)
Frontiers in Psychology | Educational Psychology June 2014 | Volume 5 | Article 603 |8

Zenner et al. Mindfulness-based interventions in schools
Table 1 | Continued
Study NAge range,
mean (SD),
grade and
gender
School/
participant
description
(country)
Study design Measures and
domain
gHedges
Baseline
equivalence
gHedges
Within-
group
gHedge
Differences
in change
scores
Reported findings according to authors
18. Schonert-Reichl
an d Law lo r , 2010
246 9–13
11.43 (1.07)
4th-7th grade
48% female
12 public
elementary
schools,
57% identified
English as their
first language,
diverse range of
socioeconomic
status (Canada)
M-group (n=139)
vs. waitlist C
(n=107)
Teachers,
instructing M in
their classes had
been assigned
randomly
Optimism (RI)
PAN AS
School
self-concept (SD)
General
self-concept (SD)
TRSC (teacher)
R
R
R
R
T
#
#
0#
0#
#
0.02#
0.02#
0#
0#
0.73#
0.27#
0.10#
0#
0#
0.73#◦
ANCOVAs on change scores: M-group showed
increase in optimism (p<0. 05) and positive affect
(p<0.10), but no decrease in negative affect. No
main effect for Group on the two self-concept
subscales, but sig. interaction effect for Group and
Age for general self-concept: Participants in grade 4
and 5 reported sig. improvement in general
self-concept, whereas controls in this age showed
sig. decreases. In contrast, M-group in grade 6 and 7
demonstrated sig. decrease in self-concept and
students in control condition increased.
ANCOVA on post-test scores: teacher ratings yielded
an sig. intervention effect on total score in all
subscales (all ps<0.001).
TWO ARMED COHORT STUDY
19. Lau and Hue,
2011
48 14–16 2 Public schools
for students
with lower
performance
(Hong Kong)
M-group (n=24)
vs. C (n=24)
SPWB
DASS
PSS
R
E
S
0.25
−0.49
−0.35
0.44
0.26
0.47
0.52
0.84
0.88
MANOVAs, ANOVAs and post-hoc tests: No sig.
effect on well-being total score (p=0.22), although
M-group had significantly higher levels at personal
growth dimension in post-test compared to
C(p=0.04). Sig. Time and Group interaction for
combining depressive symptoms and perceived
stress (p=0.01). C’s level of depression increased at
post-test (p=0.01), whereas in M-group there was
no increase (p=0.13).
NON-CONTROLLED TRIALS
20. Anand and
Sharma, in press
33 14.23
46% female
Public high
school, middle
socio-economic
status, urban
background
(Bangalore, India)
Pre-post, follow-up
after 3 months
SSS
PWI-SC
S
R
—1.64
1. 5 1
— ANOVAs: participants reported sig. reduction in
perceived stress and sig. improvement in well-being
from pre-test to post-test and from post-test to
follow-up. Detailed analysis revealed sig. changes in
5 of 7 subscales of SSS and in all of PWI-SC (no ps
reported).
21. Beauchemin et al.,
2008
34 13–18
16.16
29% female
Private residential
high school
specialized in
serving students
with learning
disorder
(Vermont, USA)
Pre-post SSRS (student)
SSRS (teacher)
STAI
R
T
E
—0.53
0.74
0.66
—T-tests: Students reported sig. reduction in state and
trait anxiety, and sig. increase in social skills (all ps<
0.05). Sig. improvements emerged for teacher
ratings on all 3 subscales (social skills, problem
behavior, and academic performance; all ps<0.05).
(Continued)
www.frontiersin.org June 2014 | Volume 5 | Article 603 |9

Zenner et al. Mindfulness-based interventions in schools
Table 1 | Continued
Study NAge range,
mean (SD),
grade and
gender
School/
participant
description
(country)
Study design Measures and
domain
gHedges
Baseline
equivalence
gHedges
Within-
group
gHedge
Differences
in change
scores
Reported findings according to authors
22. Biegel and
Brown, 2010
79 6–8
2nd +3rd grade
Elementary school
(California, USA)
Pre-post, follow-up
after 3 months
BEEDS
Sense of
Relatedness scale
Altering (ANT-C)
Orienting (ANT-C)
Executive
Control (ANT-C)
SSRS (teacher)
R
R
C
C
C
T
—0
#
0#
0#
0#
0.41#
0.16#
—ANOVAsandpost-hoc tests: Sig. improvement in
one aspect of attention (executive control; p<0.01)
form pre-test to post-test. Score stabilized from
post-test to follow-up (p=0.86). Sig. improvement
in teacher rating of social skills from pre-test to
post-test (p<0.05), which stabilized at follow-up
(p=0.75).
No other results reported.
23. Joyce et al., 2 010 141 10–13
11.4
5th +6th grade
44% female
2 primary schools
in Melbourne’s
outer suburbs
(Australia)
Pre-post,
samplesizevaried
between
Questionnaires
CDI: 120;
SDQ Diff.: 129;
SDQ Prosoc.: 141
To t al
Difficulties (SDQ)
Prosocial
behavior (SDQ)
CDI
E
R
E
—0.26
0.15
0.27
—T-tests: Participants showed sig. reductions in total
difficulties score of SDQ (p<0.00). On the prosocial
scale, only students with initially low scores
demonstrated sig. enhancement (p<0.05). Further,
students proved sig. reductions in depression levels
due to large changes in high-scoring individuals
(p<0.01) .
24. Wisner, 2008 28 15–19
17.8 6
10th-12th grade
38% female
Public alternative
high school in a
small city.
At risk of dropping
out of school.
(USA)
Pre-post BERS-2/Teacher
Rating scale
T—0.83—T-tests: According to teacher ratings, students
showed sig. improvement on behavioral and
emotional functioning (p<0.001). A sig. increase
was also revealed in each subscale (all ps<0.05).
ANOVAs: No interaction effects on gender, grade
level, and age.
#Data essential for exact calculation of effect sizes were not provided. If possible we appraised effects based on information given, as graphs for example. ◦Teachers rated improvement form pre- to post-test
after the training in M-group and Control. Between group differences were used to estimate within effect sizes as well as effect sizes of change scores. SD, Standard deviation; M-group, Mindfulness-group; C,
Control; RCT, Randomized controlled trial; ANOVA, Analysis of variance; ANCOVA, Analysis of covariance; MANOVA, Multivariate Analysis of Variance; MANCOVA, Multivariate analysis of covariance Domains: C,
Cognitive Performance; E, Emotional Problems, R, Factors of Resilience; S, Perceived Stress and Coping; T, Third Person Rating. Measures: ACTeRS, ADD-H Comprehensive Teacher Rating Scale; ANT-C, Attention
Network Test for Children; ASRES, Affective Self-Regulatory Efficacy Scale; AURE, Self-Concept and Self-Actualization Questionnaire; BEEDS, Behavioral and Emotional Engagement vs. Disaffection scale; BERS-2,
Behavioral and Emotional Rating Scale; BRIC, Behavior Rating Index for Children; BRIEF, Behavior Rating Inventory of Executive Function; CCTT, Children’s Color Trail Test; CDI, Children’s Depression Inventory;
DASS, Depression Anxiety Stress Scale; DERS, Difficulties in Emotion Regulation Scale; EP, Emotion Profile Inventory; ERS, Ego-Resiliency Scale; FBS, Feel Bad Scale; KINDL, QoL Questionnaire for Children and
Adolescents; MASC, Multidimensional Anxiety Scale for Children; PANAS-C; Positive and Negative Affect Scale for Children; PIML, People in My Life; PSS, Perceived Stress Scale; PWI-SC; Personal Wellbeing
Index—School Children; RRS, Ruminative Response Scale; RSQ, Responses to Stress Questionnaire; SCSI, Schoolagers’ Coping Strategies Inventory; SD, Self-Description Questionnaire; SDQ, Strengths and
Difficulties Questionnaire (Diff., difficulties subscales; Prosoc., prosocial behavior subscale); SICBC, Somatization Index of the Child Behavior Checklist; SMFQ-C, Short Mood and feelings Questionnaire—Child
Version; SPPC, Self-Perception Profile for Children (Global Self-Worth Subscale); SPWB, Scales of Psychological Well-Being; SSKJ, Stress and Coping Questionnaire for Children and Adolescents; SSRS, Social Skills
Rating System; SSS, School Situation Survey; STAIC, State-Trait Anxiety Inventory for Children; TASC, Test Anxiety Scale for Children; TEA-Ch, Test of Everyday Attention for Children; TIPI, Ten Item Personality
Inventory; TTCT, Torrance Test of Creative Thinking; WEMWBS, Warwick-Edinburgh Mental Well-being Scale.
Frontiers in Psychology | Educational Psychology June 2014 | Volume 5 | Article 603 |10

Zenner et al. Mindfulness-based interventions in schools
FIGURE 1 | Flow of information from identification to inclusion of studies.
a summer camp for example. Finally, four studies did not meet
methodical criteria as they used an ideographic approach (K=2)
or were case studies (K=2). Authors of two unpublished studies
which had been identified as potentially relevant in the second
screening did not provide the full-text article or data (K=1),
or could not be reached (K=1). Qualitative and quantitative
syntheses are based on all 24 studies.
GENERAL STUDY CHARACTERISTICS
Study characteristics are outlined in Tab l e 1 .Ofthe24stud-
ies that had been located, 13 were published in a peer-reviewed
journal, and three were in press. Unpublished studies comprised
manuscripts published on the internet (K=2), unpublished
data (K=1), or Master’s (K=2) and PhD dissertation theses
(K=3). The earliest study was published in 2005. Fourteen stud-
ies were carried out in North America, seven in Europe, one in
Australia, and two in Asia. In total, 1348 students were instructed
in Mindfulness, and 876 served as the comparison group, ranging
from grade 1–12, reflecting age 6 to 19. Sample sizes of studies
varied between 12 and 216. Studies differed greatly in how they
described the setting, intervention, and sample.
In eight studies, mindfulness training was implemented at ele-
mentary school level (grade 1–5), in two studies at middle school
level (grade 6–8), and in 14 studies at high school level (grade
9–12). In one study, mindfulness was introduced to students from
grade 7–12. In most studies, description of school, neighborhood,
or participants was very limited. There was a wide variety of
school types, including mostly public schools (urban and sub-
urban), a private residential school, a catholic school for girls, a
fee-paying boys’ school, a rural high school, and a public alterna-
tive high school. Where sample characteristics were mentioned,
samples were mostly of low socio-economic status and students
were described as low performing or “at risk.” However, it is
very probable that other samples might be from higher socio-
economic backgrounds, which would result in a diverse range of
sample characteristics (see Tab l e 1).
www.frontiersin.org June 2014 | Volume 5 | Article 603 |11

Zenner et al. Mindfulness-based interventions in schools
INTERVENTIONS
The programs of this database have been reviewed and rated
into different domains according to underlying theory, objectives,
components, and intensity. If an intervention is to be evaluated
in terms of effectiveness, it is necessary that details of the pro-
gram, such as the theoretical base, well defined goals, explicit
guidelines, training, and quality control, are described (Wea r e
and Nind, 2011) and steps of implementation are carefully docu-
mented (Durlak and DuPre, 2008). Not all of the studies offered
sufficient information on program details or implementation,
and some additional work was necessary to gather sufficient infor-
mation. This part of the analysis will be reported in another article
(Herrnleben-Kurz et al., in preparation). Here we summarize
basic details about interventions and programs.
As can be seen in Tab l e 2 ,thetheoretical framework of the
programs refers to the concept of mindfulness. In most cases the-
ory is linked to previously existing mindfulness programs, such
as MBSR, MBCT, DBT, and ACT. Some interventions also make
reference to theories and findings from positive psychology, or
combine MBI with a special group of school-based intervention
programs, such as social and emotional learning (SEL).
Manualized programs, such as MindfulSchools or Learning to
BREATHE, were identified in two thirds of the studies. These
programs were generally available but only two had an endur-
ing presence of more than five years, and many did not contain
sufficient guidance material for implementation. Others were
reported to be manualized, but the material was not made avail-
able (see Tab l e 2). The programs themselves often define similar
Table 2 | General features of MBI’s applied.
General features K%
THEORETICAL FRAMEWORK
Mindfulness 24 100
Positive psychology (including SEL) 9 38
Executive function 6 25
USE OF PROGRAM MANUAL
Existing since >5years(≤2007) 2 8
Existing since <5 years 13 54
Ad-hoc program 9 38
INTERVENTION FEATURES
Class by teacher 7 29
Class by non-school trainer 15 63
Class by teacher and non-school trainer 2 8
INTERVENTION COMPONENTS
Breath awareness 24 100
Working with thoughts and emotions 21 88
Psycho-education 20 83
Awareness of senses and practices of daily life 20 83
Group discussion 18 75
Body-scan 14 58
Home practice 12 50
Kindness practices 11 46
Body-practices like yoga 6 25
Mindful movement (= other body-practices) 5 21
Additional material 10 42
objectives. These are mostly related to the assessment methods and
mirrored in the domains which have been identified (see outcome
methods below).
Most programs contain more than one component to facilitate
mindfulness, with observation of breath as the traditional essen-
tial exercise, as well as psycho-education and group discussions
(see Tab l e 2).
Predominantly, MBIs were conducted by professional trainers,
most of whom were involved as study authors. Few interventions
had been instructed by the class teachers, and not all had per-
sonal experiences with mindfulness practices. Some had briefly
been introduced to the topic, while others had undergone a MBSR
course before implementation.
The periods and intensity (frequency and length) of training
varied from 4 weeks to 24 weeks with a median of 8 weeks, with
45 min once a week in most programs. Some programs split this
over several sessions per week. In total, interventions varied from
160 to 3700 min of practice, with a median of 420min.
STUDY QUALITY ASSESSMENT
As can be seen in Tab l e 1 , 19 of the 24 studies used a controlled
design and five used a pre-post design. Randomized designs
were realized in studies where mindfulness training was offered
as an alternative or extracurricular activity at school (K=10).
Students who signed up for the mindfulness training were ran-
domly allocated to either a mindfulness or control group. In
one study, a group of students with matched backgrounds was
invited to function as control. In quasi-experimental designs,
mindfulness was taught in a classroom setting and another class,
mostly the parallel class, served as control (K=8).Inanother
study (Study 17, Tab l e 1 ) a reading training of the same inten-
sity as the MBI took place. Selection and allocation of classes to
interventions was mainly decided upon by the heads and class-
room teachers. In four studies, classes or schools were randomly
assigned to conditions. Follow up measures were collected in five
studies.
Foreveryeffectsizeweperformedapost-hoc power analysis
using the software program G*Power (Faul et al., 2009). Given an
alpha of 0.05 (one-sided), and a power of 80%, a sample size of
n=41 was determined for pre-post ES to detect an effect of d=
0.40. Twelve studies met this criterion. The same procedure for
controlled ES revealed a sample size of n=78 per group, which
was achieved in three controlled studies.
Fifteen studies reported data on attrition in the intervention
group, in which rates varied between 0% (23) and around 40%
(1, 19), either due to invalid or incomplete data (7, 10, 11, 12, 13,
17, 23), or because students did not fulfill a defined amount of
attendance or home practice (1, 5, 6, 8, 19). Eight studies speci-
fied reasons for withdrawal, mostly naming scheduling conflicts,
school transfers, or school absence. Two studies reported drop-
outs due to parental refusal (12, 16) and in one case five students
decided to leave the training after the first session (19).
OUTCOME MEASURES
A variety of measures were applied to investigate the effects of
mindfulness training. We grouped the outcomes into the domains
as follows:
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Zenner et al. Mindfulness-based interventions in schools
Cognitive performance (C)
Nine measures in total were classified in the domain of cog-
nitive performance. In most cases, cognitive performance was
quantified by attention tests (Studies 8, 12, 13, 17, 22, Tabl e 1 ).
A creativity test (3) was used in one study, and in another (13) the
mind wandering paradigm was applied. Two studies (4, 6) used
grades as dependent variables.
Emotional problems (E)
In the domain of emotional problems self-report questionnaires
focusing on maladaptive emotion, cognition, and behavior are
summarized, also including clinical symptoms, such as anxiety
and depression (4, 7, 9, 12, 19, 21, 23), test anxiety (8, 12), somatic
reactions (11, 16), ruminative thinking style (11) emotion
regulation difficulties (6, 9, 11, 16), and various difficulties (23).
Stress and coping (S)
Nine Studies investigated changes of perceived stress and coping
behavior via self-report questionnaires (7, 9, 10, 13, 16, 17, 19,
20). In one study (12) cortisol measures in combination with a
stress test (math quiz) were carried out. These outcomes were
examined separately.
Resilience (R)
Seventeen studies collected self-report data on constructs we cat-
egorized as factors of resilience: well-being (13, 14, 15, 17, 19, 20),
positive and constructive emotions or affect (7, 11, 12, 13, 16, 18,
22), resiliency (14, 15), social skills and positive relationships (7,
21, 22, 23), self-concept and self-esteem (4, 5, 10, 18).
Third person ratings (T)
In the domain of third person ratings, parent and teacher ques-
tionnaires were grouped, dealing with aspects such as aggressive
or oppositional behavior, social skills, emotional competence,
well-being, attention, and self-regulation (1, 2, 6, 8, 13, 18, 21,
22, 24).
Another study measured school attendance (6). Since this
measure does not fit any of the domains, it was not included in the
domain-specific analyses. The numerical proportions of measures
applied in studies are portrayed in Figure 2.
FEASIBILITY
Only some of the studies offered information about how the
integration of the program into school-routine was working. In
some studies, one or more aspects of feasibility were assessed sys-
tematically via questionnaires, focus groups, or interviews. Some
reported a systematic assessment, but did not provide a report
or an analysis of respective data. Others reported only anecdotal
evidence.
ACCEPTABILITY
One third of studies provide information about acceptability.
There seems to be an overall high acceptability in those studies
referring to students and teachers, but, again, methods were partly
heterogeneous and unsystematic.
Results of interviews and focus groups (teachers and students)
indicate a uniformly positive experience of the intervention
FIGURE 2 | Numerical proportions of measures applied in studies.
(Beauchemin et al., 2008; Mendelson et al., 2010; Lau and Hue,
2011). Eighty-nine per cent of the students would recommend the
training to others (Broderick and Metz, 2009; Metz et al., 2013).
In Anand and Sharma’s study (in press) 81% of the students rated
the program sessions as extremely useful, and 83% as satisfying.
Three quarters of the students said that they would like to con-
tinue, and thought that it could have lasted longer (Beauchemin
et al., 2008; Huppert and Johnson, 2010), or that it was the right
length (Anand and Sharma, in press). Only 5% thought that the
intervention was too long (Huppert and Johnson, 2010). Potek
(2012) cited a noteworthy statement: “We just started getting it. I
think we should have more time to practice.”
Some of the programs also contain an individual home prac-
tice:Huppert and Johnson (2010) foundthatonethirdpracticed
at least three times a week and two thirds once a week or less. In
Broderick and Metz’s study (2009), two thirds of the participants
practiced mindfulness techniques outside the classroom. By ana-
lyzing the protocols, Frenkel et al. (in press) found that no one
practiced the full amount of weekly exercises and two thirds failed
to do their homework at least once.
IMPLEMENTATION
Joyce et al. (2010) mentioned specific factors which facili-
tated successful implementation: teaching along with colleagues,
administrative and parental support, or children’s enthusiasm.
What hindered was a lack of time and students who failed to
engage with the program. In the study of Beauchemin et al.
(2008), teachers suggested that the intervention was feasible
when conducted in a classroom with voluntary participation.
Desmond and Hanich (2010) mentioned problems regarding
scheduling, completion of administration, beginning of holidays,
and difficulties with participants arriving too late. Some studies
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Zenner et al. Mindfulness-based interventions in schools
provided information about feasibility of different program-
elements, and very few reported implementation integrity which
had been assessed via protocols, detailed scripts, feedback for-
mulas, or fidelity logs. Because these data were rare we did not
include them in the analysis of outcomes.
QUANTITATIVE SYNTHESIS
Within-group effect size
The results of the quantitative synthesis are reported in Tab le 3 .
Weighted mean effect sizes for within-group effect sizes was
g=0.41 (95% CI 0.28–0.54), which can be considered as a
small to medium effect. The Qstatistic indicates heterogene-
ity, and the I2 index shows that a large amount of variance is
caused by it. The fail-safe number exceeded the criterion. Figure 3
shows a funnel plot of the respective 24 effect sizes where the
vertical bar marks the weighted mean effect size. Asymmetry
can be seen: Studies with small sample sizes and small or even
negative effects are lacking. Only a few studies, with rather
small sample sizes, are located above the estimated mean effect
size. Sensitivity analyses, excluding the five studies with partly
Table 3 | Overall within-group and controlled effect sizes and respective subgroup effect sizes, including effect size statistics.
Type of effect size Sample Effect size τ2Homogeneity kfsaCriterionb
KnHedges’s g95%—CI pQpI
2
Within-group effect 24 1348 0.41 (0.28, 0.55) <0.00001 0.08 112.52 <0.00001 80% 1008 130
Excluding estimated ES (#) 19 917 0.49 (0.31, 0.67) <0.00001 0.12 104.86 <0.00001 83% 912 105
Excluding studies N<40 12 990 0.31 (0.18, 0.44) <0.00001 0.04 42.77 <0.00001 74% 360 70
Subgroup Franco 3 103 1.32 (1.05, 1.59) <0.00001 0.00 0.92 0.63 0% 393 25
Subgroup rest 21 1245 0.29 (0.19, 0.40) <0.00001 0.03 53.68 <0. 0001 63% 588 115
Controlled effect 19 1897 0.40 (0.21, 0.58) <0.0001 0.11 59.35 <0.00001 70% 722 105
Excluding estimated ES (#) 16 1445 0.45 (0.23, 0.68) <0.0001 0.14 54.83 <0.00001 73% 704 90
Excluding studies n<77 3 656 0.31 (0.15, 0.46) 0.0001 0.0 0.10 0.95 0% 90 25
Subgroup Franco 3 205 1.34 (1.04, 1.65) <0.00001 0.00 1.83 0.40 0% 399 25
Subgroup rest 16 1692 0.23 (0.13, 0.33) <0.00001 0.00 11.05 0.75 0% 352 90
K, number of studies; N/n, number of participants; g, weighted mean effect size; CI, confidence interval; τ2, variance component; p, level of significance; Q,
Q—Statistic. akfs is the number of unavailable studies with null results, that would be required to reduce the overall result to an insignificant level. bIf kfs is
exceeding the criterion (5k +10), an essential influence of availability bias is unlikely.
FIGURE 3 | Funnel plot of within-group effect sizes (K=24). The vertical bar represents the weighted (by sample sizes) mean effects size.
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Zenner et al. Mindfulness-based interventions in schools
estimated ES (#) from synthesis, lead to slightly higher ES (g=
0.49; 95% CI 0.31, 0.67) and more between study variance (τ2=
0.12). Synthesis only of studies with a minimum sample size of
41 (K=12) revealed an ES of.31 (95% CI 0.18, 0.44) and a
tau-squared of 0.04.
Controlled effects sizes
Weighted mean effect size of the 19 studies using a controlled
design was g=0.40 (95% CI 0.21, 0.58), a small to medium
effect. Again there was evidence for heterogeneity. The fail-safe
Ncriterion is exceeded. The funnel plot follows a similar pat-
tern of asymmetry as in pre-post effect sizes, which can be seen
in Figure 4. On the other hand, the fail-safe number of 722
exceeded clearly the criterion (105), indicating the robustness of
results concerning availability bias. Sensitivity analyses excluding
estimated ES (#) showed a similar ES (g=0.44; 95% CI 0.23,
0.68) and a larger between study variance (τ2=0.14). Synthesis
only including studies with an adequate ES of n=78 or higher
(K=3) yielded a lower ES (g=0.31; 95% CI 0.15, 0.46) and no
between study variance (τ2=0.00).
Exploratory analyses
Examining ES and plots, the three studies from the Franco Justo
research group were categorized as one subgroup. In three inde-
pendent studies, the effects of the Meditación Fluir program
were explored. This very sophisticated, demanding, and well-
established program for graduating high-school students clearly
differentiates itself from other interventions by a very high inten-
sity. A subgroup analysis was performed for within-group effect
size and controlled effect size. Separate analysis leads to a slight
reduction of heterogeneity in within-group effect sizes and to
complete reduction of heterogeneity in controlled effect sizes (see
Tab l e 3). In both cases CI intervals do not overlap, and the per-
centage of genuine subgroup differences is 98%. Differences of
subgroup effects were significant for within-group effects sizes
(χ2=50.21, p<0.00001) and controlled effect sizes (χ2=
46.47, p<0.00001).
To investigate whether the intensity of mindfulness train-
ing explains part of the heterogeneity between ES of all stud-
ies reviewed, a random-effects meta-regression was performed.
Minutes of mindfulness practice in total (including training ses-
sions and home practice, if it was compulsory) were entered
as a predictor and ES as the outcome variable. Studies were
weighted by inverse variance, combining within-trial variance
of treatment effect and the between study variance. As can be
seen in Figures 5,6, there is a substantial correlation between
ES and minutes of mindfulness training for controlled ES, and a
slightly weaker correlation for within group ES. Regression analy-
sis shows that intensity of mindfulness practice accounts for 21%
(adjusted R2=0.21) of heterogeneity in within-group ES and
52% (adjusted R2=0.52) of heterogeneity in controlled ES (see
also Tab l e 4). The three studies with the highest intensity driving
the strong correlations were those from the Spanish Franco Justo
research group.
Outcomes of quantitative synthesis for each domain are pre-
sented in Tab l e 5 . Effect sizes in the domain of cognitive per-
formance were moderate to high, whereas effect sizes of the
stress and resilience domains showed small to moderate ES.
The domain of emotional problems and third person ratings
demonstrated small ES and CI’s overlapping zero. High levels of
heterogeneity could be identified in all domains except emotional
problems. In the domain of emotional problems, heterogeneity
FIGURE 4 | Funnel plot of all controlled effects sizes (K=19). The vertical bar represents the weighted (by sample sizes) mean effect sizes.
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Zenner et al. Mindfulness-based interventions in schools
FIGURE 5 | Bubble plot of the 24 within group effects sizes against
Intensity of mindfulness Training and regression line. R2(adjusted) =
0.21.
FIGURE 6 | Bubble plot of the 19 controlled effects sizes against
Intensity of mindfulness training and regression line. R2(adjusted) =
0.52.
Table 4 | Results of random-effects meta-regression on intensity of
mindfulness training for within-group and controlled effect sizes.
Model BSE BBeta Sig.
WITHIN-GROUP EFFECT SIZE
1. (Constant)Intensity (Min_ln) −1.121 0.583 0.068
0.246 0.093 0.490 0.015
CONTROLLED EFFECT SIZE
1. (Constant)Intensity (Min_ln) −1.910 0.512 0.002
0.359 0.080 0.738 0.000
was at a medium level and according to the Q-test, absence of het-
erogeneity can be assumed. The fail-safe Ncriterion was exceeded
considerably in all 5 domains.
DISCUSSION
This is the first systematic review and meta-analysis to summa-
rize data available on the effects of mindfulness-based trainings
for children and youths in a school setting. Twenty-four stud-
ies were located that report a significant medium effect size of
g=0.40 across all controlled studies and domains. Remarkably,
the ES of studies using pre-post designs only is very similar,
with g=0.41. The effects are strongest in the domain of cog-
nitive performance with a large and significant ES of g=0.80
for controlled studies. Effect sizes are smaller but still signifi-
cant in the domains of resilience measures (g=0.36) and stress
measures (g=0.39), and they are small and not significant for
measures of emotional problems (g=0.19) and third-person
ratings (g=0.25). In the latter two domains pre-post ES are
larger, while in all other domains they are either very similar to
the controlled ES or even somewhat smaller. Thus, taken from
a bird’s eye view, mindfulness-based training in a school con-
text has effects that are seen mostly in the cognitive domain, but
also in psychological measures of stress, coping, and resilience.
Acceptance seems to be high with few reported adverse events
or incidents. There were some hints that implementation was
not always without difficulties. It is important to keep in mind
that the analysis referring to feasibility is very limited due to
methodological issues.
STRENGTHS
We went to great lengths to locate all relevant studies and get more
detailed information from authors. Since all but two authors
complied with our requests, our work is novel and complete. A
third of the material included in this review is unpublished gray
literature. Hence, we are confident that availability bias was com-
paratively small. Although the funnel plot seems to indicate such
a bias, one should bear in mind that the asymmetry is mainly
caused by three studies with large ES stemming from one group
in Spain that have developed a very intense mindfulness train-
ing. Excluding those studies from the visual analysis of the funnel
plot renders it symmetrical, thus testifying to our success at locat-
ing the most relevant studies. Also, the large fail-safe Ns show
that the results are robust regarding availability bias. In most
cases,morethantwicethenumberofavailablestudieswould
be needed to render the ES insignificant, a rather unrealistic
assumption.
We adopted conservative quantitative estimation methods.
When SD and Means were unavailable, ES of measures were set
to zero. We corrected for baseline differences by using difference-
scores as the basis of ES estimation. By using correction factors
for small studies, larger studies receive more weight, and by using
random-effects models the large variation is taken into account.
By analyzing studies both through overall ES and domain spe-
cificES,wetriedtodisentanglethemazeofverydiverseoutcome
measures employed in those studies. We took care to not inflate
ES by only using one contribution per outcome measure to each
study. Data were inspected carefully in terms of heterogeneity
and biases and various sensitivity analyses were computed. By
exploring the variation through meta-regression we were able to
account for a sizeable portion of the variance through one theo-
retically important variable, namely the amount of practice (i.e.,
the intensity) implemented in the study, which accounts for 52%
of the variance in the controlled studies and 21% of the variance
in pre-post-design studies. Given the heterogeneity of measures,
students, settings, and programs, this is a remarkable finding that
suggests that one of the most important factors for the variation
across studies is the amount of practice that a mindfulness based
program has introduced.
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Zenner et al. Mindfulness-based interventions in schools
Table 5 | Domain specific effect sizes and statistics for within group and controlled effects sizes respectively.
Domain Type of effect size Sample Effect size Heterogeneity
KnHedges’s g95%—CI I2
Cognitive performane pre-post 8 327 0.68 (0.33, 1.03) 88%
Controlled 7 569 0.80 (0.35, 1.26) 82%
Emotional problems pre-post 11 693 0.31 (0.19, 0.42) 44%
Controlled 9 903 0.19 (−0.03, 0.41) 52%
Stress pre-post 8 374 0.36 (0.05, 0.66) 85%
Controlled 7 674 0.39 (0.07, 0.71) 78%
Factors of resilience pre-post 17 1082 0.38 (0.20, 0.55) 86%
Controlled 13 1497 0.36 (0.09, 0.62) 82%
Third person Ratings pre-post 8 448 0.34 (0.08, 0.60) 84%
Controlled 6 591 0.25 (−0.10, 0.61) 74%
K, number of studies; n, number of participants; g, weighted mean effect size; CI, confidence interval.
LIMITATIONS
This is simultaneously the major limitation of our findings: the
heterogeneity of the studies is considerable, and hence the esti-
mates of effect sizes, including their significance, can only have an
orienting function. It is plausible that school-background, social
background, and how a program is accepted within a particu-
lar school context influence its effects, yet we do not have the
information necessary to explore these effects or those of other
potential moderators. For instance, it is a completely different sit-
uation if pupils attend within the compulsory school framework
or are willing to stay on in their free time, whether there is a class-
room or workshop setting. Furthermore, it makes a difference
if teachers themselves implement programs or if outside train-
ers come and deliver the courses. Additionally, the instructors’
qualifications and their personal experience with mindfulness are
surely important. A lot of this information may be decisive, yet is
not available in study reports.
As is the case with any nascent field of research, the hetero-
geneity is also built in through the exploratory framework of most
studies. In only a few cases, such as with the Franco Justo research
group, were studies conducted in replication. Mostly, researchers
implemented their own programs. Therefore, a variety of pro-
grams were evaluated or tested. Thus, there are no manualized
consensus programs available, as is the case with MBSR or MBCT.
Also, outcome measures for children are much less stable, both
psychometrically and age-wise. By default, a lot of tests available
for children are only partially validated, or are sometimes used
in age groups where no clear validation exists. Also, some of the
measures might have exhibited floor or ceiling effects, especially
when clinical measures are used for groups that are within nor-
mal range. While the motivation of patients studied in clinical
studies of MBSR and MBCT is comparatively easy to gauge, such
a motivation is less clear for children. This source of variance was
completely out of reach for us, as only one study documented
motivation.
Studies are often underpowered and small. This is not a sur-
prise, given the exploratory nature of the field. It means, however,
that the findings are tentative and need to be supported by larger,
more robust evaluations in groups that are representative of
settings where such trainings will likely be implemented. It also
means that a large proportion of the effect size is derived from
studies where the study size is small and hence the variation is
large. Synthesis only including studies with an appropriate sample
size revealed an ES of.31 for pre-post as well as controlled ES. The
decrease in ES and heterogeneity indicates that our results might
be slightly biased by the “small-study effect” (Sterne et al., 2000),
which leads to an overestimation of ES. As a result, an overall ES
of 0.31 is a more stable estimate.
None of the studies used a strong active control. Hence the
ES estimate is for an effect which has not been compared with
another intervention or control. The precise role the element of
mindfulness really plays is unknown, as is the extent of the effect
that can be attributed to non-specific intervention factors, such as
perceived group support, the specialty, and novelty of the inter-
vention, of taking time out in school and at home, or of generic
resting and relaxing. We only have one indirect indicator, and
this is the strong correlation between ES and mindfulness training
intensity revealed by the meta-regression.
COMPARISON WITH OTHER FINDINGS
This is the first analysis of its kind regarding school based MBIs, as
far as we are aware. Meta-analyses have been carried out in other
fields, such as the clinical effects of MBSR in adults (Grossman
et al., 2004). This first analysis isolated an ES of approximately
d=0.5, for patients and non-patients, for physical and mental
health measures alike. In a more recent meta-analysis by Eberth
and Sedlmeier (2012) an ES of r=0.31 was found for the effect
of MBSR in non-clinical adult populations, based on a larger
amount of studies (k=17). Thus, effects of MBIs in non-clinical
settings seem to be slightly higher in adults than in children and
youth.
However, the ES we derived in this analysis are in the same
range as results of other meta-analyses of school-based pre-
vention programs. A meta-analysis of school-based social and
emotional learning programs, for example, revealed an overall
ES of g=0.30 and an I2 of 91% (Durlak et al., 2011). Also,
the ES of 3 domains, namely emotional problems, resilience,
and third person ratings, showed similar ES compared to
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Zenner et al. Mindfulness-based interventions in schools
respective categories in larger meta-analyses of school-based pre-
vention programs. However, effects on academic achievement
were lower in other meta-analyses (Durlak et al., 2011; Sklad
et al., 2012). ES of stress and coping measures were much
higher (g=−1.51) in studies targeting stress directly than in
this study (Kraag et al., 2006). Levels of statistical heterogene-
ity of the referred studies were about the same magnitude as in
our study.
SUGGESTIONS FOR FURTHER WORK
It is obvious that more research, especially larger and randomized
studies, if possible with active controls, is needed. Also, longer
follow-up measures would be appropriate, primarily to see if
benefits are lasting, but also to investigate potential effects of
triggering developmental steps. Besides, attrition rates, includ-
ing reasons for dropout, should be reported, because relevant
information regarding implementation strategies, feasibility, and
contraindication might be extracted. Great consideration must
be given to outcome measures. As our analysis shows, the
effects of mindfulness-based interventions can be rather dif-
ferentiated across domains. A lot of the scales used are not
really adequate. Researchers might want to pilot their measures
before using them or employ measures that have been sensitive
in other studies. Further, it would make sense not to exclu-
sively rely on self-report data and questionnaires in general,
but to triangulate measures with qualitative data and behav-
ioral measures. Using qualitative approaches, new hypotheses
could be generated and other adequate methods could be devel-
oped. Manuals of the intervention studied should be made
available.
To prevent unnecessary failure in implementation, studies
should use a mixed-methods approach to assess outcome and
acceptability, adopting methods such as written teacher reports,
review sessions, individual interviews, observations of training
sessions and student questionnaires and interviews. For exam-
ple, Greenberg et al. (2004) have described a number of criteria
such as timing, dosage and quality of sessions, student absen-
teeism and responsiveness, teacher experience, and commitment.
It should be determined which aspects of the implementation
process are most important, and what adaptations can be made
without harming the integrity of the intervention. All this can
only be investigated if adequate information is provided. This
will allow future meta-analysts to assess sources of heterogeneity
better than we were able to.
What