Using Spacing to Enhance Diverse Forms of Learning:
Review of Recent Research and Implications
Shana K. Carpenter &Nicholas J. Cepeda &Doug Rohrer &Sean H. K. Kang &
Published online: 4 August 2012
#Springer Science+Business Media, LLC 2012
Abstract Every day, students and instructors are faced with the decision of when to study
information. The timing of study, and how it affects memory retention, has been explored for
many years in research on human learning. This research has shown that performance on
final tests of learning is improved if multiple study sessions are separated—i.e., “spaced”
apart—in time rather than massed in immediate succession. In this article, we review
research findings of the types of learning that benefit from spaced study, demonstrations
of these benefits in educational settings, and recent research on the time intervals during
which spaced study should occur in order to maximize memory retention. We conclude with
a list of recommendations on how spacing might be incorporated into everyday instruction.
Keywords Memory .Distributed practice .Spacing effect
One fundamental decision that students and instructors must make is when to study
information. If students learned new information yesterday, should they begin to review
their notes today, or wait a few more days? Once instructors have presented information,
how long should they wait before they review this information in order to increase the
chances that students will retain it over summer break? Given that the intended outcome of
Educ Psychol Rev (2012) 24:369–378
S. K. Carpenter (*)
Department of Psychology, Iowa State University, W112 Lagomarcino Hall, Ames, IA 50011, USA
N. J. Cepeda
Department of Psychology and LaMarsh Centre for Child and Youth Research, York University, Toronto,
Department of Psychology, University of South Florida, Tampa, USA
S. H. K. Kang
Department of Education, Dartmouth College, Hanover, USA
Department of Psychology, University of California, San Diego, USA
such decisions is to promote durable learning, understanding how the scheduling of study
influences memory retention is critically important.
The Benefits of Spaced Study
Studying information across two or more sessions that are separated (i.e., spaced apart or
distributed) in time often produces better learning than spending the same amount of time
studying the material in a single session. Figure 1illustrates the design of a typical study on
this topic. This design includes: (1) multiple study sessions in which the same information
(e.g., biology terms) is presented at least twice, (2) a manipulation of the time duration
between successive presentations, which is referred to here as the spacing gap, and (3) a test
delay that is defined as the time elapsed between the final study presentation and the test.
The test delay can either be fixed or manipulated.
When the spacing gap between two or more presentations of the same item is zero (e.g.,
the same biology term and definition is presented back-to-back with no interruptions in-
between), the presentations are said to be massed together. When the gap between presenta-
tions is greater than zero (e.g., a given biology term is repeated every 5 min or after five
different biology terms have been presented), then the presentations are said to be spaced or
distributed because they are separated by a nonzero time interval. The gap separating spaced
presentations can range anywhere from a few seconds to several weeks, whereas the gap
separating massed presentations is zero.
On the final memory test, performance is most often better for items that were spaced
rather than massed. This is typically referred to as the spacing effect. Some studies have also
reported that different spacing gaps (i.e., lags) result in different degrees of learning, which
has sometimes been referred to as the lag effect. For example, learning of a given biology
term might be better when it is repeated after a relatively long spacing gap (e.g., 5 min)
compared to a relatively short spacing gap (e.g., 1 min). In the current paper, we use the term
spacing effect in a general sense to refer to the different degrees of learning that result as a
function of different spacing gaps.
The spacing effect is one of the oldest and most reliable findings in research on human
learning. Early demonstrations of this effect date back to over 100 years ago (e.g., see
Ebbinghaus 1885/1913), and hundreds of published studies have reported benefits of spacing
(for a recent review, see Cepeda et al.2006). While participants in most of these studies were
adult learners, the benefits of spacing have also been reliably demonstrated in studies with
younger participants, including elementary school children (e.g., Toppino & DiGeorge 1984),
middle school children (e.g., Carpenter et al.2009; Toppino & DeMesquita 1984), and preschool
children as young as 3 or 4 years of age (e.g., Rea & Modigliani 1987; Toppino 1991).
Fig. 1 Design of a typical study on the spacing effect. Participants experience two learning sessions that are
separated by an interval of time referred to here as the spacing gap. After another interval of time called the
test delay, participants are given a final test over the information that they encountered in the two learning
370 Educ Psychol Rev (2012) 24:369–378
The vast majority of studies on the spacing effect have been conducted in the laboratory,
and these studies typically require participants to learn relatively simple types of verbal
information such as word lists or trivia facts. Recently, however, new findings have emerged
showing that spacing can also improve learning of information that is conceptually more
difficult. For example, Bird (2010) found that longer spacing gaps improved English-learning
adults’understanding of subtle grammatical rules. Participants saw sentences such as “Albert
Einstein has been a great mathematician,”and their task was to provide the corrected version,
“Albert Einstein was a great mathematician.”Two practice sessions were separated by either 3
or 14 days, and the 14-day spacing gap produced superior scores to the 3-day gap on a test given
60 days later. Spacing has also been shown to improve learning in other tasks that might be
considered complex forms of learning, such as spelling (Fishman et al.1968), reading skills
(e.g., Seabrook et al.2005), and biology (Reynolds & Glaser, 1964).
Spacing effects were found in two recent experiments in which college students learned a
moderately abstract mathematics task (Rohrer & Taylor 2006,2007). The task required
students to find the number of permutations of a sequence of items with at least one repeated
item. For instance, the sequence abbccc has 60 permutations, including cabcbc and abcbcc.
In both studies, spacing boosted scores on a final test consisting of novel problems of the
same kind. Figure 2shows the results of one of these studies.
Benefits of spacing have also been reported for tasks involving coordinated motor skills. For
instance,inastudyreportedbyMoultonet al.(2006), surgical residents practiced microsurgical
skills in four training sessions that were squeezed into the same day or distributed across
4 weeks. On a final test given 1 month after the last practice session, a spacing effect was found.
Recent studies have shown that spacing can benefit learning in realistic educational
contexts as well. In one study, Sobel et al.(2011) investigated fifth-graders’retention for
the definitions of uncommon English words of the type that appear on the Graduate Record
Examination (e.g., abscond: to leave secretly and hide, often to avoid the law). These words
were learned in class via a teacher-led tutorial that included slides, oral practice, and paper-
and-pencil tests. Either immediately or 1 week after the first tutorial, students completed the
same tutorial a second time, and were then given a final vocabulary test that required them to
supply the definition for each word 5 weeks after completing the second tutorial. Memory on
of one kind
5 more problems
of the same kind
10 problems of
the same kind
1 or 4 wks
Test Delay (weeks)
Fig. 2 A mathematics spacing experiment. College students observed a tutorial on how to solve an obscure
kind of permutation problem before attempting 10 practice problems that were given in a single session (0-day
spacing gap) or spaced across two sessions separated by 1 week (7-day spacing gap; for full details, see Rohrer
& Taylor 2006). A test with novel problems of the same kind was given 1 or 4 weeks later. Spacing had no
reliable effect on test scores after a 1-week delay but doubled test scores after a 4-week delay
Educ Psychol Rev (2012) 24:369–378 371
the 5-week delayed test was superior for definitions learned with the 7-day spacing gap
(20.8 %) compared to the 0-day spacing gap (7.5 %). This amount of forgetting might appear
substantial, but previous research on forgetting of classroom material has demonstrated a
similar level of forgetting over a similar time period (Jones 1923; Tiedeman 1948).
In a second study, Carpenter et al.(2009) explored how the timing of a review session
affected retention of US history facts that were learned by eighth grade students. After
completing their course in US history, students completed a review activity that involved
answering several questions from the most recent unit that they studied (e.g., Who assassi-
nated president Abraham Lincoln?). For each question, students were asked to write an
answer (e.g., John Wilkes Booth), and then were given a sheet of answers to check their
accuracy. One group of students completed the review 1 week after finishing the course (i.e.,
the Immediate Review Group), and another group completed the same review 16 weeks
later, after returning from summer vacation (i.e., the Delayed Review Group). Students were
tested over the information again 9 months after completing the review. After such a
substantial delay, it is not surprising that students forgot the majority of answers to these
questions. The key finding, however, was that long-term retention was better for students
who completed the delayed review than for those who completed the immediate review
(12.2 vs. 8 %, respectively).
Another demonstration of the benefits of spacing in the classroom was reported by
Seabrook et al.(2005), who assessed first graders’acquisition of reading skills. In their
regular classrooms, all students received 6 min of instruction per day for 2 weeks. One group
of students received this instruction within a single session lasting 6 min, while a second
group received it across three separate 2-min sessions that were administered at unspecified
time intervals. A comparison of pretest and posttest scores revealed that the group experi-
encing the spaced 2-min sessions showed greater improvement in reading skills (an increase
of 8.3 points), compared to the group experiencing the continuous 6-min session (an increase
of only 1.3 points).
How Long Should the Spacing Gap Be?
To use spacing as effectively as possible, it is important to know just how far apart the study
sessions should be spaced. For instance, if medical professionals wish to maintain good
retention of emergency response skills over a 2-year period, is there an optimal time during
which they should review these skills? When learners must retain information over a given
test delay, an important practical questiontoaddressiswhenrepeatedstudyofthis
information should take place.
If spacing benefits learning, then a reasonable assumption might be that longer spacing
gaps would benefit learning to an even greater degree. Indeed, some studies examining the
effects of longer vs. shorter spacing gaps have typically found that longer spacing gaps are
more beneficial for retention (e.g., Glenberg 1976; Hintzman 1969,1974; Melton 1970). For
example, Kahana and Howard (2005) found that retention of words was best when the words
were repeated three times with 6–20 other words occurring between each of the three
presentations, compared with only two to six other words occurring between each of the
Studies by Bahrick and colleagues examining long-term retention appear to confirm the
idea that longer spacing gaps produce better memory retention than shorter spacing gaps. In
a study by Bahrick (1979), participants learned the English translations for several Spanish
words by completing six learning sessions that were separated by a spacing gap of either
372 Educ Psychol Rev (2012) 24:369–378
0 days (i.e., all sessions occurred on the same day), 1 day, or 30 days. All participants were
given a final test 1 month after the lastlearning session. Performance on this test was best for the
participants who learned the words with the 30-day spacing gap. A follow-up study revealed
that retention of these words after 8 years was still superior for the participants who experienced
the 30-day spacing gap relative to the 0- or 1-day spacing gap (Bahrick & Phelps 1987).
However, reviews of the literature on spacing have revealed that an increase in the
duration of the spacing gap does not always produce superior memory retention (e.g.,
Cepeda et al.2006,2009; Donovan & Radosevich 1999; Glenberg 1976; Verkoeijen et al.
2008). One potential danger of waiting too long before reviewing information is that
students may forget much of what they have learned previously, and this forgetting may
offset any benefits that would have occurred due to spacing. This suggests that there may be
diminishing returns to increasing the spacing gap.
What might the optimal spacing gap be? Answering this question requires a thorough
comparison of the effects of different spacing gaps across a wide range of time intervals. In
what was probably the most comprehensive study ever to explore this, Cepeda et al.(2008)
gave adult learners a flashcard-like web tutorial in which they learned a set of obscure facts
(e.g., Libya’s flag consists of a single solid color). During the first learning session, participants
learned 32 of these facts until they could recall each of them successfully. Then, each participant
completed a second learning session in which they were quizzed over each fact (e.g., what
country’s flag consists of a single solid color?), and then shown the answer (e.g., Libya).
Finally, each participant was given a final test over each fact in which they were shown this
question again and asked to recall the answer. The spacing gap between the two learning
sessions ranged across several values between 0 and 105 days. For example, some participants
completed the two learning sessions with a 2-day spacing gap, others with a 7-day gap, and
others with a 21-day gap. Following the second learning session, each participant completed the
final test after a test delay of 7, 35, 70, or 350 days. Each participant was randomly assigned to
one of 26 unique combinations of spacing gap and test delay.
Figure 3shows the proportion of facts correctly recalled on the final test as a
function of spacing gap and test delay. The key finding from this study is that the
Fig. 3 Proportion of facts recalled in the study by Cepeda et al.(2008) as a function of spacing gap (either 0,
1, 2, 4, 7, 11, 14, 21, 35, 70, or 105 days) and test delay (either 7, 35, 70, or 350 days). The spacing gap that
produced the highest level of recall was dependent upon the test delay, such that shorter spacing gaps (e.g.,
1 day) were more beneficial for recall after a relatively short test delay (e.g., 7 days), and longer spacing gaps
(e.g., 21 days) were more beneficial for recall after a longer test delay (e.g., 70 days)
Educ Psychol Rev (2012) 24:369–378 373
optimal spacing gap depends on when the information will be tested in the future. For
participants who completed the final test 7 days after their final study session, the
optimal spacing gap was 1 day. However, for participants who waited 35 days before
taking the final test, the optimal spacing gap was 11 days. For those who completed
the final test after 70 days, the best spacing gap was 21 days. In general, the optimal
spacing gap equaled 10–20 % of the test delay. In other words, the longer the test
delay, the longer the optimal spacing gap.
This study demonstrates that there is no “one-size-fits-all”approach to using spacing as a
means of improving memory retention. Quite simply, a longer spacing gap is not always
better. Instead, these findings suggest that in order to pick the optimal timing of study
sessions, students and instructors must decide when they expect to need the information. If
the goal is to retain information for just a short time, shorter spacing gaps may be ideal.
However, if the goal is to achieve retention for much longer periods, spacing gaps of several
weeks or months may be best. Indeed, for lifelong preservation of knowledge, spacing gaps
of years may well be optimal.
While the study by Cepeda et al.(2008) sought to determine the optimal duration of a
spacing gap when learning is limited to only two sessions, numerous studies have addressed
a related question: if learners encounter information in three or more sessions, should the
spacing gaps be equal? Studies that have explored the effects of different spacing gaps with
three or more learning sessions have typically compared two schedules of spacing: (1) a
fixed schedule, in which all spacing gaps are identical (e.g., information is studied four
times, with a 24-h spacing gap separating each study session) or (2) an expanding schedule,
in which the spacing gap becomes progressively longer (e.g., information is studied once,
then again after 30 min, then a third time after 24 h, and a fourth time after 1 week).
Experiments comparing fixed and expanding schedules have produced equivocal results.
Some studies have found that expanding schedules produce better learning than fixed
schedules (e.g., Cull et al.1996; Landauer & Bjork 1978), and others have found that
expanding and fixed schedules produce similar levels of learning (e.g., Carpenter & DeLosh
2005; Cull 2000; Logan & Balota 2008; Pyc & Rawson 2007; for a critical review of this
literature, see Balota et al.2007).
Recent evidence suggests that expanding schedules might be better for short-term
retention, and fixed schedules might be better for longer-term retention (Karpicke &
Roediger 2007). A comprehensive comparison of various spacing gaps and test delays
involving three or more learning sessions has yet to be carried out and until then, it remains
an open question whether the optimal spacing gaps for three or more learning sessions are
critically dependent upon when the final test takes place.
One finding appears to be reliable, however. Any form of spacing—whether it is fixed or
expanding—appears to promote learning. In studies comparing either a fixed or expanding
schedule to a massed schedule in which three or more presentations of an item occur back-
to-back in immediate succession, it has been consistently demonstrated that either type of
spacing schedule produces better learning than a massed schedule (e.g., Carpenter & DeLosh
2005; Cull 2000; Rea & Modigliani 1985).
Thus, when faced with the practical question of when to review information, the present
findings suggest that students and teachers do not need to be overly concerned about
whether the spacing gaps that separate repeated study sessions are equal or not. The key
criterion is that information should be reviewed after a period of time has passed since the
initial learning. Particularly if the goal is long-term retention, the findings from Cepeda et al.
(2008) suggest that the ideal time to review information may be several weeks or months
after it was initially learned.
374 Educ Psychol Rev (2012) 24:369–378
Pedagogical Recommendations and Responses to Potential Challenges
Many researchers have urged teachers and curriculum designers to use spacing as an
instructional strategy (e.g., Bahrick 1979;Bjork1979;Dempster1987,1988,1989;
Halpern 2008; Metcalfe et al.2007; Pashler Rohrer et al.2007; Willingham 2002).
Unfortunately, however, spacing has yet to be systematically implemented in educational
curricula (e.g., Cepeda et al.2008; Dempster 1988; Rohrer & Pashler 2010). One reason for
this could be that research on spacing has not produced a clear set of recommendations for
how it can be used in everyday instruction. In this section, we describe some specific
strategies that can be used by students and educators to capitalize on the advantages of
The literature reviewed here suggests that in order to promote long-term retention of
knowledge, students should receive spaced re-exposure to previously learned information.
Particularly if the goal is long-term retention, it may be beneficial to review this information
after a time period of at least several weeks (e.g., Cepeda et al., 2008). This review can take
place in a number of ways. First, instructors might incorporate into each lesson a brief
review of concepts that were learned several weeks earlier.
Second, homework assignments could be used to re-expose students to important infor-
mation that they have learned previously. This recommendation may be particularly useful
when class time is limited and a review is difficult to fit in to the lesson on any given day.
For example, an instructor could intentionally include questions covering information that
was learned in class several weeks earlier.
Third, instructors could give exams and quizzes that are cumulative. In addition to re-
exposing students to information that they have previously learned, cumulative exams and
quizzes provide students with a good reason to review information on their own. These three
recommendations are not mutually exclusive, and like any guidelines, they are more likely to
produce positive learning outcomes when used in conjunction with one another (for more on
pedagogical recommendations involving spacing, see Pashler et al.2007a,b).
These recommendations may sometimes be difficult to carry out. First, students often
seem to be less than enthusiastic about cumulative exams. When the exam is cumulative,
students may feel that there is more information that they must study. However, if students
are provided with regular reviews of previously learned information, this information is
more likely to remain accessible in memory, reducing the need for them to restudy old
information that has already been forgotten.
Second, instructors may be discouraged to find that after several weeks, students have
forgotten much of the information that they had previously known. It is commonly the case
that students forget a good deal of what they have learned, especially after lengthy time
periods (e.g., Carpenter et al.2008; Dillon 2008). Importantly, however, this is not an
indication that the instruction was wholly futile. On the contrary, when students are re-
exposed to information that they have learned but temporarily cannot recall, they acquire this
information much faster than information that is being learned for the first time (e.g., Berger
et al.2008; Ebbinghaus 1885/1913; Nelson 1985). Thus, although forgetting is likely to be a
necessary consequence of reviewing information after long spacing gaps, re-exposing
students to this information on a regular basis will keep it accessible in memory and render
it less vulnerable to forgetting over time.
A final challenge that instructors might encounter in implementing spacing into learning
curricula is the fact that educational materials appear to discourage this approach. In
particular, many textbooks present information in a nondistributed fashion. For instance,
although spacing has been known to improve foreign-language learning (e.g., Bahrick et al.
Educ Psychol Rev (2012) 24:369–378 375
1993; Bahrick & Phelps 1987; Bird 2010; Bloom & Shuell 1981), in most foreign language
textbooks, the vocabulary of each chapter is devoted to a particular topic (e.g., food,
clothing), and these words rarely appear in subsequent chapters. Likewise, in most mathe-
matics textbooks, each set of problems is devoted to the most recent lesson. After learning
about ratios, for example, students will work one or two dozen ratio problems.
Because textbooks do not typically provide spaced exposure to concepts, in order to
ensure that students receive this, instructors may find it necessary to supplement the
information from any given lesson with examples from previous lessons. For example, in
one rarely used approach to mathematics learning, each lesson is followed by an interleaved
set of examples from many different lessons. Interleaving inherently provides spaced
practice, and, no less importantly, it also provides students with an opportunity to choose
the appropriate strategy for a given kind of problem, which students need not do when every
problem concerns the same procedure or concept (e.g., Rohrer 2009; Taylor & Rohrer 2010).
In this review, we have highlighted some key findings concerning the types of learning
that benefit from spacing, demonstrations of spacing effects in educational settings, and
explorations of the ideal spacing gap. We have also attempted to shed some light on how the
benefits of spaced practice might be implemented in everyday instruction. We hope that this
information can be of value to students and educators who are seeking ways of using spacing
to maximize learning.
Acknowledgments This work was supported by a collaborative activity award from the James S. McDonnell
Foundation, by the Office of Naval Research (grant N00014-10-1-0072), by the Institute of Education
Sciences (US Department of Education grant R305B070537 to H. Pashler and grant R305A110517 to D.
Rohrer), and by the National Science Foundation (Center Grant SBE-0542013).
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