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ORIGINAL RESEARCH
published: 03 June 2015
doi: 10.3389/fpsyg.2015.00705
Edited by:
Emily Mather,
University of Hull, UK
Reviewed by:
Caspar Addyman,
Birkbeck, University of London, UK
Natalia Arias-Trejo,
Universidad Nacional Autónoma
de México, Mexico
Hester Elizabeth Duffy,
University of Warwick, UK
*Correspondence:
Karin Keller,
Department of Psychology
and Human Development,
UCL Institute of Education, University
College London, 20 Bedford Way,
London WC1H 0AL, UK
k.keller@ioe.ac.uk;
Larissa M. Troesch,
Department of Psychology, University
of Basel, Missionsstrasse 60/62,
4055 Basel, Switzerland
larissa.troesch@unibas.ch
†These authors have shared first
authorship.
Specialty section:
This article was submitted to
Developmental Psychology,
a section of the journal
Frontiers in Psychology
Received: 17 February 2015
Accepted: 12 May 2015
Published: 03 June 2015
Citation:
Keller K, Troesch LM and Grob A
(2015) First-born siblings show better
second language skills than later born
siblings.
Front. Psychol. 6:705.
doi: 10.3389/fpsyg.2015.00705
First-born siblings show better
second language skills than later
born siblings
Karin Keller1,2*†, Larissa M. Troesch1*†and Alexander Grob1
1Department of Psychology, University of Basel, Basel, Switzerland, 2Department of Psychology and Human Development,
UCL Institute of Education, University College London, London, UK
We examined the extent to which three sibling structure variables number of
siblings,birth order, and presence of an older sibling at school age are linked
to the second language skills of bilingual children. The research questions were
tested using an ethnically heterogeneous sample of 1209 bilingual children with
German as a second language. Controlling for children’s age, sex, nationality,
number of children’s books at home, family language and parental German language
skills, hierarchical regression analyses showed an inverse relationship between the
number of siblings and second language skills: the more siblings a child had, the
lower was his/her second language proficiency. This relationship was mediated by
attendance in early education institutions. Moreover, first-born siblings showed better
second language skills than later born siblings. The current study revealed that the
resource dilution model, i.e., the decrease in resources for every additional sibling,
holds for second language acquisition. Moreover, the results indicate that bilingual
children from families with several children benefit from access to early education
institutions.
Keywords: birth order, sibling, second language acquisition, language proficiency, bilingualism
Introduction
Despite the constant decline in number of children in families, the ideal of the two-child family
still persists (Testa, 2012) and it is generally assumed that siblings mutually enrich and learn from
one another (Howe and Recchia, 2006). In the case of families from immigrant backgrounds, the
assumption is furthermore that older siblings play an important role in integrating the family into
the host culture and constitute a facilitator particularly to the language of the host country (Cooper
et al., 1999;Shin, 2002).
Language skills, which are the focus of the present study, cover semantic, syntactic, morphologic
and pragmatic facets (Saxton, 2010) and are considered as a crucial prerequisite to be successful
in and after school. Studies indicated that there is a gap between language skills of immigrant
and non-immigrant children starting in early childhood, which does not close even after years
of schooling (e.g., Oller and Eilers, 2002). Local language oftentimes implies a second language
for immigrant children. Second language skills are acquired in a broad range of developmental
contexts that include interactions with educators in early education institutions, with children
and adults in the neighborhood as well as interactions within the family (Hoff, 2013). Research
regarding familial contexts in the scope of second language acquisition has been sparse so far with
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Keller et al. Sibship in bilingualism
existing studies mainly focusing on parental influences (e.g.,
Becker, 2010). However, empirical evidence of whether and how
sibling structure variables are associated with second language
skills of children is still pending.
Thus, the present study examines the effect of sibling structure
variables on the second language skills of immigrant children.
In particular, we investigated whether classic models of sibling
structure variables such as the resource dilution model can
be applied to second language acquisition. These research
questions are addressed in a large sample of bilingual children
in Switzerland.
The Resource Dilution Model
Educational studies of the past 50 years report that only children
and children with fewer siblings achieve better grades at school
and have a higher level of education than individuals from
families with many children (e.g., Blau and Duncan, 1967;
Park, 2008). The resource dilution model explains this inverse
relationship between number of siblings and number of years
in education with a decrease in parental resources (Blake, 1981).
This model is based on the assumption that parental resources
are finite and have to be shared between children within a
family. Every additional sibling means a reduction in the share
allocated to each child, thus reducing one of the foundations
of their intellectual development. According to Blake (1981),
parental resources include material resources, extra-familial
learning opportunities, and parental attention, intervention and
teaching. The strength and the pattern of the relationship vary
depending on the type of resource (Downey, 1995, 2001). Some
resources, such as a stock of books for example, can be shared
between several siblings without any significant reduction in
their value. By contrast, financial resources, invested by parents
in a child’s extracurricular education for example, appear to be
more vulnerable to the number of siblings (Downey, 1995, 2001;
Steelman et al., 2002). According to the resource dilution model,
parental resources available do not decline linearly with every
additional child. Rather, the decline in parental resources as the
number of children within a family increases comes closest to the
theoretical equation y=1/x(Downey, 1995), where xrepresents
the total number of children in the family and yrepresents the
parental resources available such as financial resources for early
education institutions.
Effect of Number of Siblings
Theeffectsofsibshipsizebecomeparticularlyclearwhen
measuring school success and education indicators such as
number of school years (Blake, 1981;Iacovou, 2007), but they can
also be seen in studies on standardized intelligence and language
measures (Belmont and Marolla, 1973;Polit and Falbo, 1988;
Steelman et al., 2002;Sundet et al., 2010). A comparison of non-
verbal and verbal measures in Polit and Falbo’s (1988) review
revealed a greater vulnerability in the field of language.
Research into sibling effects on second language acquisition
is sparse. It therefore remains unclear whether and in which
way the number of siblings is linked to the second language
skills of bilingual children, and whether the effects of diminishing
parental resources can be seen in a way that is analogous to
first language development. Given a greater degree of direct
interaction between parents and child in families with fewer
children (Jones and Adamson, 1987), we assume that children
from smaller families benefit more from parents’ knowledge
of the local language (when extant) or indirectly gain a better
foundation for acquiring a second language through better
support in the first language (e.g., reading picture books
together; Verhoeven, 1994;Uchikoshi, 2006). Based on Downey’s
(1995) finding that financial resources have a particularly strong
tendency to dilute and the knowledge that children pose a risk of
poverty (European Commission, 2008), we assume that families
with many children have fewer financial resources to provide
educational opportunities outside the family and therefore, the
likelihood of a child attending early education institutions is
lower.
As early education institutions constitute key places for the
second language acquisition of immigrant children (Aukrust and
Rydland, 2011;Niklas et al., 2011;Halle et al., 2012), we suppose
that limited access to these institutions has a negative effect on
the second language development, i.e., attendance in an early
education institution is assumed to mediate the relationship
between the number of siblings and second language skills. This
mediational effect is all the more plausible as access to the
early childcare system in Switzerland and some other European
countries is limited and parental costs for institutional childcare
are high (OECD, 2013).
Although knowledge to date suggests that an inverse
relationship exists between the number of siblings and second
language skills among bilingual children according to the
resource dilution model, no evidence exists confirming this
assumption. Ortiz (2009), for example, examined 747 Latino
preschool children in the USA assessing English language skills
by means of a standardized receptive language test. In Ortiz’s
study, contrary to the author’s expectations, there was no
association between the number of children and knowledge of
English language skills.
Effect of Birth Order
During their early years of life — or at least their first year —
first-born children do not have to share parental attention and
financial resources for early education institutions with their
younger siblings. Thus, based on the resource dilution model it
can be assumed that first-born children have an advantage over
later-born siblings during childhood. Various studies have shown
that there are differences favoring first-born children both in
regard to the onset of speech and in regard to level of language
skills (Pine, 1995;Zambrana et al., 2012). In Fenson et al.’s (1994)
large-scale study first-born children showed greater abilities in
word production in both infancy and toddlerhood. The Swedish
study of Berglund et al. (2005) with over one thousand 18-
months-old children revealed significant negative effects of birth
order on both the production and the comprehension of words.
However, the strength of these effects was minimal, with an
explained variance of 1.7% in vocabulary production and 0.5%
in vocabulary comprehension respectively. Based on a study with
pairs of siblings, Pine (1995) showed that first-born children
achieve the 50-word milestone roughly a month earlier than their
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Keller et al. Sibship in bilingualism
second-born siblings. However, no significant differences were
found for the 100-word milestone some months later. Differences
in the amount and the kind of parental input were assumed to
be the reason for the differences between first- and later-born
siblings. Studies showed that first-born children are read to more
often than later born children (Raikes et al., 2006;Westerlund
and Lagerberg, 2008), that these children receive more linguistic
input from their mothers, and that the children are more often
explicitly encouraged to express themselves (Jones and Adamson,
1987;Hoff-Ginsberg, 1998).
Although some studies revealed a negative effect of birth order,
there are also studies, that found no differences in standardized
language tests or even suggested that later-born children are at an
advantage (Jenkins and Astington, 1996;Oshima-Takane et al.,
1996;Hoff-Ginsberg, 1998;Bornstein et al., 2004;Westerlund
and Lagerberg, 2008). For example, Oshima-Takane et al. (1996)
showed that later-born children used personal pronouns earlier,
which the authors attributed to more frequent triadic interactions
with the mother and the elder sibling. Hoff-Ginsberg (1998)
reported disadvantages in vocabulary and grammar in later-
born children, but also noted a developmental advantage in
conversational skills.
The extent to which birth order is associated with second
language skills among immigrant children remains unclear. On
the one hand, it is conceivable that mechanisms similar to those
in monolingual children are at work, and that higher second
language skills can be expected in first-born children during
their first few years due to their situation as only children.
On the other hand, it has been repeatedly reported that older
siblings constitute a facilitator to the local language (e.g., Shin,
2002) and that second-born children accordingly have been
expected to experience more favorable conditions of acquisition
and have better second language skills. This advantage might be
particularly true for children with an older sibling in school age.
To become an effective language partner, older siblings need to
possess a certain level of second language skills. In school age,
children improve their second language skills und thus pose a
significant source of language exposure to the younger sibling
(Bridges and Hoff, 2014). Moreover, at school, older siblings
learn the importance of local language skills and bring that
knowledge into the home. Younger siblings might profit from
the insights and second language skills of their older siblings and
thus, improve their local language skills (Wong Fillmore, 1991;
Shin, 2002).
These two approaches — the resource dilution model as well
as elder siblings as facilitators for the second language acquisition
of their younger siblings — explain the issue on different levels
and are not mutually exclusive. Thus it is conceivable that while
the processes of interaction between siblings benefit learning,
the arrival of an additional sibling changes the relationship
constellation and the financial situation of a family to such an
extent that the second-born child is placed at a developmental
disadvantage.
To date, evidence for both lines of arguments is sparse and
mixed. Ortiz (2009) assumed better second language skills for
later-born children, but failed to demonstrate evidence in a group
of Latino preschool children in the USA. No effect of birth order
on knowledge of the second language emerged either in David
and Wei’s (2008) longitudinal study with 13 French- and English-
speaking children nor in Caspar and Leyendecker’s (2011) study
with 88 Turkish-German-speaking children. Bridges and Hoff
(2014) also examined older siblings’ influence on language skills
in a total of 87 English–Spanish bilingual toddlers in the USA
assessing English and Spanish language skills using caregiver
report measures. In contrast to the previous findings, in their
study, children with an older sibling showed more advanced
English language skills. Moreover, bilingual children with an
older school-aged sibling were more skilled in English.
In sum, the current state of research is marked first by a lack of
studies on sibling structure variables among immigrant children
and, second, by mixed results. Thus, further studies are needed to
shed light on the significance of siblings on second language skills
of bilingual children.
The Current Study
The current study examined the extent to which three sibling
structure variables, — i.e., number of siblings, birth order and
presence of an elder sibling at school age — are connected to
the second language skills of bilingual children, and whether
theresourcedilutionmodelcanbeadoptedtothesecond
language acquisition of immigrant children. First, we postulated
an inverse relationship between the number of siblings and
second language skills. Second, we examined whether attending
an early education institution mediates the relationship between
number of siblings and second language skills referring to the
resource dilution model (Blake, 1981;Downey, 1995, 2001).
Third, we examined whether, in analogy to studies on early
first language development, better second language skills can be
expected of first compared to later-born children (e.g., Zambrana
et al., 2012), or whether, conversely, later-born children benefit
from their older siblings and show higher levels of second
language skills (e.g., Shin, 2002;Zambrana et al., 2012). To
complement the third hypothesis, we examined whether the
effect of the birth order depends of the age gap to the older
sibling. We assumed that later-born children have higher levels
of second language skills if the older sibling is already at school
age and can thus be expected to possess better German and better
communication skills (Bridges and Hoff, 2014).
Materials and Methods
Procedure
The data of this study stem from the Basel research project
Zweitsprache [Second Language]. One goal of the project
Zweitsprache was to develop a parental questionnaire to assess
German language skills of immigrant children. Another goal
was to examine the educational and care situation of children
from immigrant backgrounds and analyses their developmental
trajectory from pre-school to first grade. The sample was
recruited in Basel, a city with 194,000 inhabitants in the German-
speaking part of Switzerland.
The study was based on a parental questionnaire sent to all
families in Basel with a child between two-and-a-half and 3 years
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Keller et al. Sibship in bilingualism
of age in the years 2009, 2010, 2011, and 2012. The questionnaire
was employed three-and-a-half years before the children started
school. The Basel-Stadt statistical office provided the addresses to
which the questionnaire was posted. Parents were able to either
completethequestionnairethemselvesathomeortotakepart
in an information event, where trained assistants with a Bachelor
degree in psychology and/or intercultural intermediaries assisted
in filling out the questionnaires. Of the 4,739 conveyed forms,
2,608 were returned, 131 could not be delivered, and 2,000 have
not been sent back.
The study was audited by the Ethic Review Committee of the
City and the County of Basel (EKBB) and approved as ethically
unobjectionable.
Sample
The present study included only children with German as a
second language and children with German as a bilingual first
language. The total sample consisted of 1,209 children (47.7%
girls) aged between 32 and 45 months (M=38.9, SD =3.7). The
children originated from Switzerland (39.5%), former Yugoslavia
(10.8%), Turkey (9.9%), Italy (5.3%), Portugal (4.1%), India
(3.0%), Germany (2.6%), Sri Lanka (2.5%), Spain (2.2%), UK
(2.2%), and 62 further countries with frequencies <2%.
A majority of the children (81%), 11.3% of mothers and 12.8%
of fathers were born in Switzerland. The average length of the
stay in Switzerland for parents born abroad was 10.45 years for
mothers and 12.84 years for fathers, respectively. In 31.5% of
families, only the native language was spoken at home, in 26.4%
the native language was usually spoken, in 38.5% the native
language and German in equal measure, in 5.0% usually German
and in 1.3% only German was spoken.
Measures
German Language Skills
Language skills contain semantic, syntactic, morphologic, and
pragmatic facets and are regarded as a complex system of rules
(e.g., Saxton, 2010). In the current study German language
skills were assessed using the standardized parental questionnaire
DaZ-E (Keller and Grob, 2013), which covers receptive as well
as productive aspects of language skills with special emphasis
on semantics and pragmatics. The questionnaire consists of
17 items. For example, parents had to answer the following
questions: “How often does your child say something in German
(e.g., to parents, other children, relatives etc.)?” [0 =never,
1=rarely, 2 =sometimes, 3 =often] or “Does your child
understand the following questions in German?” “Wo ist das
Fenster?” [English translation: “Where is the window?”],“Wasist
dein Lieblingsessen?” [English translation: “What’s your favorite
food?”], “Wie gross bist du?” [English translation: “How tall are
you?”],[0 =no/I cannot rate, 1 =yes]. The items add up to a sum
score that is linearly transformed to a scale with a range from 0
(low)to10(high).
The questionnaire exists in Albanian, Bosnian/Serbian/
Croatian,German,English,French,Italian,Portuguese,
Spanish, Tamil, and Turkish. The different language versions
of the questionnaire have been checked for measurement
invariance (RMSEA =0.042; RMSEA =0.009; CFI =0.944;
CFI =0.008). The questionnaire versions have a reliability
of Cronbach’s αof 0.92 to 0.97, a concurrent validity with the
Language Development Test SETK-2 (Grimm, 2000) of 0.84, and
a test–retest reliability of 0.95 over a period of 4 months (Keller
and Grob, 2013).
Sibling Structure Variables
Sibling structure variables were assessed at the same time
as language skills. Parents provided information about the
individuals living in the same household and on the years of birth
of any siblings. Thirty-nine percent (n=472) of the sample were
only children at the time of the survey, 42.7% (n=516) had one
sibling, 13.3% (n=161) two siblings, and 5.0% (n=60) three
or more siblings (Ta b le 1 ). The variable number of siblings was
transformed according to the formula of the resource dilution
model −1/x(x=number of children; Downey, 2001). In order to
examine the number of children at which unfavorable effects can
be expected to set in, we formed three dummy variables: dummy
1: no siblings (=1) versus at least one sibling (=2); dummy 2:a
maximum of one sibling (=1) versus more than one sibling (=2);
dummy 3: a maximum of two siblings (=1) versus more than two
siblings (=2).
Regarding the variable birth order, a distinction was made
between first-born children (n=677; 56.0%) and later-born
children (n=532; 44.0%). Only and first-born children were
both included in the category first-born children, as comparable
intelligence and language scores can be expected according to
Polit and Falbo’s (1988) review. 10.8% of the children had at least
one sibling that was 1–3 years older, 19.2% had one or more
siblings 3–6 years older, 10.5% had one or more siblings 6–9 years
older, 6.6% of the children had at least one sibling that was 9–
12 years older and 5.9% had at least one sibling that was 12 or
more years older.
The variable children with an older sibling at school age
constituted a subcategory of the category later-born children and
referred to children with at least one older sibling with an age gap
of 3 or more years. Based on the Swiss school enrolment system,
which has a cut-off date, it was possible to deduce that these were
TABLE 1 | Descriptives, mean, and standard deviation of German language
skills.
Language skillsa
n%MSD
Sib size
Only child 472 39.0 4.70 3.27
Two children 516 42.7 4.71 3.28
Three children 161 13.3 4.79 3.23
Four or more children 60 5.0 4.18 2.59
Birth order
First-born 677 56.0 4.78 3.35
Later-born 532 44.0 4.58 3.09
Older sibling at school age
No older sibling at school age 817 67.6 4.81 3.31
Older sibling at school age 392 32.4 4.43 3.06
aSum scores of the German language questionnaire DaZ-E (Keller and Grob, 2013).
Frontiers in Psychology | www.frontiersin.org 4June 2015 | Volume 6 | Article 705
Keller et al. Sibship in bilingualism
children with a sibling at school age (n=392; 32.4%). Sixty-eight
percent of the sample (n=817) had no older sibling at school age.
Early Education Institution
In the current study, an early education institution is defined
as an institution that offers childcare for children before
kindergarten entry. In the city of Basel, kindergarten is
mandatory and starts at age 4. There are different forms of
early educational care such as playgroups or daycare centers.
These forms vary in educational concepts as well as opening
hours.
Attendance in an early education institution was assessed
using parental questionnaires. Parents stated the name of the
institution and the weekly length of care in numbers of hours.
The average length of care, which served as a mediator in
this study, was 10.7 h per week (SD =13.1, range: 0–55 h).
The medium length of two to three half-days per week in the
sample corresponds to the length of care expected in Switzerland,
but is clearly lower than the average hours of care in the
USA (31 h/week) and other European countries such as France
(31 h/week) or Germany (23 h/week; OECD, 2013, 2014).
Control Variables
The information about the children’s sex, age, and nationality
was provided by the Basel-Stadt statistical office. The variable
nationality was divided according to national languages into
1=countries where German is the national language and
2=countries where German is not the national language. The
mother’s German skills and the father’s German skills were each
measured using an item with a four-point scale in the parental
questionnaire (1 =nonexistent,4=well). The control variable
family language was ascertained using the question Does your
family speak predominantly German at home or another language?
(1 =Exclusively German,5=Exclusively another language;Keller
and Grob, 2013). As a proxy for the home language and linguistic
environment the number of children’s books in the household
was recorded (1=up to 10; 2 =up to 20; 3 =up to 30; 4 =more
than 30).
Statistical Procedure
First, we calculated measures of descriptive statistics. Second, in
order to examine the effect of three sibling structure variables, —
i.e., number of siblings, birth order, and presence of an elder
sibling at school age — on German language skills, we conducted
hierarchical regression analyses. In each hierarchical regression
analysis, the variable German skills was the dependent variable
and, in a first step, the control variables sex, age, nationality,
number of children’s books, family language, German skills of
the mother and German skills of the father were entered, which
are important predictors for second language skills (e.g., Becker,
2010). In a second step, the sibling structure variables were added
(hypotheses 1 and 3).
The second hypothesis focused on the mediation effect of
the length of attendance in an early education institution
on the relationship between the number of siblings and
German skills. In order to test a mediation effect, the data
has to meet the following precondition (a) the effect of the
independent variable (in this case: number of siblings) on
the mediator (in this case: length of attendance in an early
education institution) and (b) the effect of the mediator on
the dependent variable (German skills) need to be statistically
significant (Baron and Kenny, 1986). In case these preconditions
are met, the mediator has to significantly reduce the effect
of the independent variable on the dependant variable. One
statistical procedure to test whether the mediator significantly
reduces the effect of the independent variable on the dependant
variable is the Sobel test. It tests whether the indirect
effect of the independent variable on the dependent variable
through the mediator variable is significant (Baron and Kenny,
1986).
Results
Descriptive statistics of German skills are displayed in Ta b l e 1 .
The bivariate correlations of number of siblings, birth order and
presence of an older sibling at school age resulted in correlations
with high effects (r=0.63–0.78), which was expected given the
conceptual overlap between these three dimensions. Thus the
likelihood of an older sibling at school age is greater for children
with a higher number of siblings; indeed, it is only possible for
later-born children to have older siblings of school age.
The first hypothesis on the effect of the number of siblings
was tested using a hierarchical regression analysis with German
skills (second language of the children) as a dependent variable.
In the first step and in all subsequent analyses, the control
variables considered were: sex, age, nationality, number of
children’s books, family language, German skills of the mother,
and German skills of the father. The second step was to
include the target variable number of siblings in the model. This
variable had been transformed previously into −1/xaccording
to the resource dilution model (Downey, 1995, 2001). The eight
variables included in the model explained 38% of the variance in
German skills [R2=0.379, F(8,1208) =93.32, p<0.001]. In line
with our hypothesis, the variable number of siblings produced
a significant negative effect on German skills [R2=0.002,
F(1,1200) =4.61, p<0.05, β=−0.05; Tab l e 2 ]. The more
siblings a child had, the lower his/her German skills. However,
the variable number of siblings explained only 0.2%. In a further
analysis intended to test the number of children at which
unfavorable effects can be expected to set in, the number of
siblings was included in the model using three dummy variables.
Again, in a first step the control variables were included in
the hierarchical regression analysis. In the second step, the
threedummyvariableswereincluded.Thedummyvariable
no siblings versus at least one sibling produced a significant
effect (β=−0.05, p<0.05, one-tailed), whereas the other two
dummy variables a maximum of one sibling versus more than
one sibling (β=−0.00, p=0.92) and amaximumoftwo
siblings versus more than two siblings (β=−0.01, p=0.83)
were unable to explain any additional variance in German
skills.
The second hypothesis aimed to test the mediation effect of
the length of attendance in an early education institution on the
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Keller et al. Sibship in bilingualism
TABLE 2 | Effect of number of siblings and length of attendance in an early education institution on German language skills.
German language skills
Model 1 Model 2a
Predictors Step 1 Step 2
βTp βTp βTp
Constant −1.85 0.07 −2.32 <0.05 −1.90 0.06
Sex 0.02 0.66 0.51 0.01 0.61 0.54 0.02 1.08 0.28
Age 0.15 6.63 <0.001 0.16 6.80 <0.001 0.13 6.67 <0.001
National language −0.03 −1.13 0.26 −0.03 −1.09 0.28 −0.04 −0.77 0.08
Number of children’s books 0.36 15.55 <0.001 0.36 15.62 <0.001 0.22 10.30 <0.001
Family language −0.28 −10.69 <0.001 −0.28 −10.73 <0.001 −0.29 −12.85 <0.001
Mothers’ German language skills 0.22 8.14 <0.001 0.22 8.13 <0.001 0.17 7.50 <0.001
Fathers’ German language skills 0.07 2.75 <0.01 0.07 2.91 <0.01 0.13 5.71 <0.001
Number of siblings −0.05 −2.15 <0.05 −0.01 −0.39 0.70
Length of attendance 0.42 19.48 <0.001
R20.002 0.149
corrR2(Total) . 0.378 0.379 0.535
aStep 2 of the hierarchical regression analysis including control variables and Length of attendance; Sex: 1 =male, 2 =female; National language: 1 =countries where
German is the national language, 2 =countries where German is not the national language; family language: 1 =exclusively German, 5 =exclusively another language.
relationship between the number of siblings and second language
skills. A regression analysis following the procedure of Baron
and Kenny (1986) was applied. Again, the variables sex, age,
nationality, number of children’s books, family language, and
parental German skills were entered first as control variables. The
preconditions of significant effects of (a) the independent variable
number of siblings on the mediator length of attendance in an
early education institution [R2=0.010, F(1,1183) =13.91,
p<0.01, β=−0.10] and (b) the mediator on the dependent
variable German skills [R2=0.151, F(1,1181) =386.13,
p<0.001, β=0.42] were met. I.e., the more siblings a child
had, the fewer hours the child attended an early education
institution and the more hours a child attended an early
education institution, the better his/her German skills. Taking the
variable length of attendance into account, 54% of the variance in
German skills was explained [R2=0.535, F(9,1188) =152.75,
p<0.001]. The variable length of attendance itself explained 15%
of the variance [R2=0.149, F(1,1180) =379.64, p<0.001,
β=0.42; Tab l e 2 ]. By taking the mediator into consideration, the
aforementioned direct effect of the number of siblings on German
skills was reduced by 84% [R2<0.001, F(1,1180) =0.15,
p=0.70, β=−0.01]. The Sobel test resulted in a significant
effect (z=3.50, p<0.001). Thus the mediation of the length of
attendance in an education institution was confirmed in line with
the resource dilution model.
The third hypothesis focused on the effect of birth order on
second language skills and was also tested using a hierarchical
regression analysis. The control variables were entered in a first
step and the independent variable birth order (1 =first-born,
2=later-born) in a second step. The variables included in
the model explained 38% of the total variance [R2=0.381,
F(8,1208) =94.05, p<0.001]. The predictor birth order had
a significant negative effect on German skills [R2=0.004,
F(1,1200) =8.21, p<0.01, β=−0.07; see Ta b l e 3 ], which
persisted when the control variable number of siblings was taken
into consideration [R2=0.002, F(1,1199) =3.58, p<0.05
one-tailed, β=−0.07]. The results matched the resource dilution
model and confirmed that first-born children possess better
second language skills than later-born children, regardless of the
number of siblings. The competing hypothesis, which assumed
that older siblings had a positive effect and ascribed a bridging
function to them, was not supported.
The hypothesis that children with an older sibling at school
age had a linguistic advantage over those without an older
sibling at school age could not be confirmed. The variable
older sibling at school age did not significantly explain variance
in German skills when the aforementioned control variables
and the number of siblings were taken into consideration
[R2=0.002, F(1,1199) =3.26, p=0.07; β=−0.05; see
Tab l e 3 ].
Discussion
On the basis of a sample of over 1,200 bilingual children, the
current study examined whether and how the number of siblings,
birth order and presence of an older sibling at school age were
associated with second language skills. To do this, two contrasting
theoretical approaches, the resource dilution model and the theory
of siblings as a facilitator to the local language,wereexamined.
As postulated in the first hypothesis, lower second language
skills were identified when the number of siblings increased. In
line with the resource dilution model, the greatest detriment
to second language skills occurred when a first sibling was
added. However, the effect size was small. The presence of
a second or third sibling did not have statistically significant
influence on the second language skills of the target child.
Even though this result conforms to the theory and the
Frontiers in Psychology | www.frontiersin.org 6June 2015 | Volume 6 | Article 705
Keller et al. Sibship in bilingualism
TABLE 3 | Effect of birth order and older sibling at school age on German language skills.
German language skills
Predictors Model 1aModel 2b
βTp βTp
Constant −1.32 0.19 −1.32 0.19
Sex 0.01 0.53 0.60 0.01 0.58 0.57
Age 0.15 6.70 <0.001 0.15 6.57 <0.001
National language −0.03 −1.04 0.30 −0.02 −0.92 0.36
Number of children’s books 0.36 15.50 <0.001 0.36 15.19 <0.001
Family language −0.28 −10.82 <0.001 −0.28 −1.89 <0.001
Mothers’ German language skills 0.22 8.29 <0.001 0.22 8.24 <0.001
Fathers’ German language skills 0.07 2.88 <0.01 0.07 2.92 <0.01
Number of siblings −0.02 −0.53 0.60
Birth order −0.07 −2.86 <0.01
Older sibling at school age −0.05 −1.81 0.07
R20.004 0.002
corrR2(Total) 0.381 0.381
aStep 2 of the hierarchical regression including control variables and Birth order; bStep 2 of the hierarchical regression including control variables and Older sibling at
school age; Sex: 1 =male, 2 =female; National language: 1 =countries where German is the national language, 2 =countries where German is not the national
language; family language: 1 =exclusively German, 5 =exclusively another language; birth order: 1 =1=first-born, 2 =later-born; Older sibling at school age: 1 =no
sibling at school-age, 2 =sibling at school age.
basic formula 1/x(Downey, 1995, 2001), it does to a
certain extent contrast with some studies on the effects of
siblings among monolingual children. Thus the review of
Polit and Falbo (1988) showed that a growing risk of lower
linguistic and cognitive performance only exists for families
with three or more children, not two. The mixed results
regarding the question from which number of children upward
detrimental effects exist may be due to families’ financial
situation and their position in society. In the current study,
immigrant families were examined, most of which have less
financial resources at their disposal and a lower status in
society than native families (Bundesamt für Statistik [BFS],
2008).
To the authors’ knowledge this is the first study able to
examine the assumption that attendance in an early education
institution mediates the relationship between the number
of siblings and second language skills. According to our
study, the resource dilution model can be generalized to
families of bilingual children. The inclusion of the mediator
length of attendance in an education institution reduced
the direct effect of the number of siblings on the second
language by 84%. This means that with an increasing number
of siblings, the hours of attendance in early education
institutions decreased. The length of attendance in an early
education itself constituted a significant predictor of second
language skills explaining 15% in second language skills.
Taking the length of attendance in an early education
institution into account, the examined variables explained a
considerable amount of variance in second language skills
(54%).
Although the current study indicates that the resource
dilution model can be generalized to the second language
acquisition of immigrant children, the significance of different
kinds of parental resources may differ for native families and
families from immigrant backgrounds. According to Downey
(1995), for native families intrapersonal resources such as
frequency of conversations within the family and educational
aspirations as well as the financial resources invested in
educational establishments and learning materials are of central
importance. By contrast, for the second language acquisition
of immigrant children it appears that financial resources
invested in extra-familial learning opportunities are a key
component. This may be connected to the lower level of
parental skills in the local language, which cannot be passed
on directly to the children and instead needs to be bought
in the form of education and learning activities (Becker,
2010).
We also examined whether older siblings represented more
of an opportunity or a disadvantage for second language
acquisition. The current study showed that children without
older siblings had better second language skills than children
with an older sibling, regardless of whether that sibling
was already at school or not. As has been ascertained
for the first language (Pine, 1995;Berglund et al., 2005;
Zambrana et al., 2012), first-born children had a developmental
advantage with regard to second language acquisition too.
This advantage is small but in a similar range as has been
shown in previous studies investigating monolingual children
(e.g., Berglund et al., 2005). We can assume that the changes
in family constellation following the arrival of a sibling
alter the family interaction mechanisms (Strohschein et al.,
2008). For example, time for dyadic interaction is reduced
(Jones and Adamson, 1987). According to Tomasello and
Farrar (1986), it is precisely these dyadic interactions in
which the focus of attention does not have to be shared
that are particularly valuable for building vocabulary (Mannle
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Keller et al. Sibship in bilingualism
et al., 1992). The extent to which this explanation can be
applied to multilingual families is unclear. In families where
the local language is spoken alongside the native language,
mechanisms similar to those in the first language development
are conceivable. For families that use only the native language
at home, contact with playmates, which is possibly initiated
more frequently and consciously by parents for a first-
born child than for later-born children, represents a possible
explanation.
As the two theories of resource dilution and siblings as
a facilitator to the local language refer to different levels
(economic versus intrapersonal level), we cannot preclude that
both mechanisms occur simultaneously. Even though this study
was unable to provide evidence of beneficial effects of older
siblings, these may occur nonetheless but may not become
apparent due to the existence of negative effects of parental
resource dilution.
A further explanation for why no positive effects of older
siblings have been found may be the age of the older siblings.
Thus it is conceivable that the older siblings of the three-and-
a-half-year-old children have only been at school for a short
time, and that their own knowledge of the second language
is thus too little developed to be of help to their younger
siblings (Oller et al., 2011). Possibly, the advantageous effects of
older siblings become more evident in older children. Whether
older siblings take on a beneficial role for younger children
at a later point and then represent a facilitator to the local
language and culture is matter that further studies would need
to examine.
Strengths, Limitations, and Future Research
To date, there are only few studies that examine how
sibling structure variables are associated with second language
acquisition. By researching this connection, the present study
provides an important contribution to understanding the
development conditions of bilingual children.
One of the study’s main strengths is its sample size, which
made it possible to include a great number of control variables,
such as sex, age, nationality, family language, and parental
German skills. Furthermore, it was possible to test the effect of
the number of siblings, something that has frequently posed a
problem for previous studies with smaller samples (e.g., Kessler,
1991, cited in Iacovou, 2007).
Despite the strengths, some limitations have to be mentioned.
One limitation is the study’s cross-sectional approach, which
precludes any statements on effect direction. In their longitudinal
study with monolingual families, Rodgers et al. (2000) addressed
this question. They showed that it is not the birth order
that affects children’s cognitive outcomes, but that parents
with lower cognitive skills tend to have more children. In the
present study we controlled for parental skills. But despite
controlling for these third variables, the question of whether
family form really is the reason for lower second language skills
remains unanswered and need to be addressed in longitudinal
studies.
Another limitation lies in the between-families design.
Although sib size is a measure of differences between families,
birth order effects are a measure of processes within families
(Rodgers et al., 2000). Therefore, the most appropriate way of
investigating birth order effects, i.e., comparing elder siblings
to their younger siblings, lies in studying sibling pairs in a
longitudinal within-families design.
German language skills were measured only by parental
report. Even though the parental questionnaire used to assess
German skills is highly valid (r=0.84 with a standard
German language test), language tests would provide an more
precise picture on language skills. Moreover, the studies of
Hoff-Ginsberg (1998)andBornstein et al. (2004) suggest that
there may be differences in the effect of sibling order for
different measurements of language, e.g., parental questionnaire
versus language tests. Thus parental perception of developmental
processes and the higher attention paid to developmental changes
in first-born children in comparison to later-born children may
have been an issue. Thus, it would be interesting to use language
test data as dependent variables in future analyses.
Based on the knowledge that siblings take on different roles
depending on culture, we assume that the effects and the strength
of effects vary across cultures. In cultures that involve older
children more strongly in bringing up their younger siblings
(Cicirelli, 1994;McGuire and Shanahan, 2010), positive sibling
effects on second language acquisition are conceivable. Hence,
designing a comparative cultural study would be useful to test this
for both first and second language acquisition.
Conclusion
In sum, the present study was able to show that the resource
dilution model can be applied to the second language acquisition
of immigrant children. Even though parental resources may
not be relevant to first and second language acquisition in the
same way, there appears to be an analogy to the first language
acquisition in regard to the educational investments made (extra-
familial learning opportunities, according to Blake (1981).
Considering that families from immigrant backgrounds have
fewer financial resources (Bundesamt für Statistik [BFS], 2008),
and that these resources influence the children’s level of
development (Mistry et al., 2008), it seems all the more important
that immigrant families with many children are financially
supported so that their children are offered the best opportunities
possible for their academic careers. Given the results of this study,
promoting the attendance of early education institutions is an
efficient way of achieving this goal.
Acknowledgments
The study was supported by the Office of Education of the
city of Basel and the Swiss National Science Foundation
(no. P2BSP1_151879). We would like to thank the families
for their interest and giving their time to participate in the
research project. Furthermore, we wish to acknowledge the
collaboration of the research assistants and the intercultural
intermediaries during data collection, and Laura Wiles for
manuscript proofreading.
Frontiers in Psychology | www.frontiersin.org 8June 2015 | Volume 6 | Article 705
Keller et al. Sibship in bilingualism
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Conflict of Interest S tatement: The authors declare that the research was
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