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World of Labor
Evidence-based policy making
TENY MAGHAKIAN SHAPIRO
Santa Clara University, USA
The educational effects of school star t times. IZA World of Labor 2015: 181
do i: 10.15185/iz awol .181
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Teny Maghakian Shapiro ©
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Pros
Hours of sleep are positively correlated with
academic achievement, yet traditional secondary
school schedules lead to sleep deprivation among
adolescent students.
Starting classes later in the morning improves
grades in classes throughout the day and boosts
standardized test scores.
Even small adjustments in start time can have
benecial effects.
Lower-ability students gain the most from delayed
start times.
Delaying start times can be a very cost-effective
measure for raising student achievement.
ELEVATOR PITCH
The combination of changing sleep patterns in adolescence
and early school start times leaves secondary school
classrooms lled with sleep-deprived students. Evidence
is growing that having adolescents start school later in
the morning improves grades and emotional well-being,
and even reduces car accidents. Opponents cite costly
adjustments to bussing schedules and decreased time after
school for jobs, sports, or other activities as reasons to
retain the status quo. While changing school start times is
not a costless policy, it is one of the easiest to implement and
least expensive ways of improving academic achievement.
AUTHOR’S MAIN MESSAGE
Because adolescents have different internal clocks than younger children and adults, and later natural sleep and waking
times, early secondary school start times are not conducive to learning. Empirical studies nd sizable gains in test scores
and grades from later start times for adolescents. A one-hour delay has the same effect as being in a class with a third fewer
students or with a teacher whose performance is one standard deviation higher. Later start times are also shown to improve
non-academic outcomes, such as mood and attendance, and reduce the frequency of automobile accidents. While changing
start times is not costless, the benets are likely to outweigh the costs.
Cons
An optimal start time for secondary schools has not
been determined.
Starting school later will require ending school
later, reducing the amount of time available for
homework, jobs, and extracurricular activities.
School districts that rely on one set of buses to
serve all different levels of schools—e.g. elementary,
middle, and high schools—may need to purchase
additional buses or change the start time for the
other school levels.
Reduced time for extracurricular activities may
require scheduling adjustments or additional
expenses.
The educational effects of school start times
Delaying secondary school start times can be a cost-effective policy
to improve students’ grades and test scores
Keywords: start times, biorhythms, sleep, secondary education, education production function
KEY FINDINGS
A one-hour delay in school start times is associated with
a 2.32 percentage point increase in test scores
Source: [1].
6
4
2
0
−2
Percentage point
change in test score
−1.0 −0.5
Slope = 2.32
0.00.5
Change in school start time
1.0
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World of Labor
Evidence-based policy making
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Evidence-based policy making
MOTIVATION
Sleep–wake cycles are governed by the circadian rhythm, a hard-wired “clock” in the
brain that controls the production of the sleep-inducing hormone melatonin. In the
early 1990s, researchers discovered that adolescents experience major changes in their
circadian rhythm, with an approximately three-hour shift toward later bed and wake-up
times, making 7.30 a.m. for an adolescent equivalent to 4.30 a.m. for an adult [2]. Ideally,
students whose school starts early would go to bed early to ensure a full night’s sleep.
However, because of this delay in circadian rhythm, adolescents are unable to fall asleep
early enough to get eight or nine hours of sleep before they need to wake up for school,
leading to an increase in daytime sleepiness. In much the same way, a typical adult would
struggle to fall asleep at 8.00 p.m. in order to wake up at, say, 4.00 a.m. the next morning.
Thus, traditional school schedules affect adolescent sleep patterns by forcing adolescents
to wake up and learn at a time when their bodies want to be asleep. A systematic review of
adolescent sleep patterns across the world shows a linear trend toward later school-night
bedtimes from age 11 to age 18 [3]. The majority of the students examined were deemed
to be sleep-deprived after age 13.
Schools have spent a lot of money on improving student outcomes. They have hired
better teachers, reduced class size, increased their use of technology, and changed class
content and pedagogy, among other measures. Delaying school start times to better align
with adolescents’ sleep–wake cycles offers sizable benets to students’ academic and
emotional outcomes at a relatively low cost.
DISCUSSION OF PROS AND CONS
Adolescents all around the world start their school day early in the morning, at a time
when their bodies prefer to be asleep. For example, in the US, most adolescents begin
their school day around 7.30 a.m., several hours before their bodies are ready to wake up
and begin the day’s activities. Studies from multiple disciplines and from many countries
have indicated that early school start times lead to sleep deprivation among students and
that hours of sleep are positively correlated with academic achievement [4]. While both
correlational and anecdotal evidence point toward the benets of later school start times,
the causal relationship between start times and academic achievement has only recently
been studied.
Empirical studies on sleep time and school start time
A few studies have looked at how time of day affects student performance. Scores on
intelligence tests are signicantly lower in the early morning hours for adolescents, which
suggest that adolescents’ circadian rhythms affect their ability to learn and perform [5].
This hypothesis is supported by research that nds that college students perform better
in classes that meet later in the day [6]. Similarly, in Chicago public high schools, both
attendance and achievement are signicantly lower in rst-period classes than in other
periods; this effect is particularly strong for mathematics classes [7]. While these studies
begin to shed light on the relationship between time of day and learning, the estimated
effects are likely biased due to students’ ability to select their classes. Students may choose
to take a class with a friend or a class that is taught by an instructor they particularly like,
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Evidence-based policy making
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Evidence-based policy making
or they may decide to schedule most of their classes during their preferred times of day for
learning. Thus, these studies cannot tell us about the causal relationship between school
start times and student academic achievement.
There are just a handful of empirical studies that have specically assessed the academic
effects of school start times. Despite the fact that these studies are based in the US,
correlational research on start times and global sleep patterns give us no reason to believe
that these ndings are unique to US students. Most of these studies take advantage of
natural experiments based on exogenous changes in school start times. Two studies use
the start time change in Minneapolis public high schools from 7.15 a.m. to 8.40 a.m.,
which was introduced in the 1997/1998 school year. The rst study examined course
grades earned by students attending Minneapolis high schools in the three years before
and the three years after the start time change and found a small, but statistically non-
signicant, improvement [8].
Grading often has a subjective component, and therefore grades are not easily comparable
across instructors or time, the study admits the challenge that arises in measuring
academic success with this metric. The second study examining the change in start times
in Minneapolis looked at students’ ACT (American College Test) exam scores instead. The
study compared the ACT scores of students in Minneapolis to those of students in St.
Paul, Minneapolis’s “twin city,” where start times had not changed, and found that the
later start times had no effect [9]. Although the ACT is scored more objectively than class
assignments and tests, the exam correlates quite highly with general cognitive ability [10].
Since later school start times cannot change students’ innate ability, a delayed start time
would not be expected to show any effect on ACT scores.
Another study aimed to answer this question by looking at end of the year standardized
mathematics and reading test scores in middle schools in Wake County, North Carolina.
School start times varied from 7.30 a.m. to 8.45 a.m. as a result of idiosyncrasies in school
boundary changes and bus scheduling [1]. These differences enabled the study to explore
the effect of later start times by comparing outcomes across schools with different start
times and within schools that experienced a change in start time (some were assigned
earlier start times while others were assigned later ones). The study nds that an increase
in start times by one hour leads to a three percentile point gain in both mathematics and
reading test scores for the average student.
A study analyzing course grade data for rst-year students at the US Air Force Academy
found similar results [11]. Several characteristics of the academic setting there allow for a
compelling study of the effects of start time. First, the Air Force Academy had two changes
in start times. Classes initially started at 7.30 a.m. They were then moved to 7.00 a.m. and
later to 7.50 a.m. Second, students at the Air Force Academy are randomly assigned to
their classes and professors during their rst year, which eliminates the issue of students
selecting into certain classes or class times. Additionally, all students take standardized
exams for their core classes, and grading is standardized across all instructors teaching
the same course in a given semester. Finally, attendance is mandatory for all classes.
Figure 1, which presents the distribution of students’ grades across the three different
start times, shows that the later the start time, the higher the distribution of grades. The
statistical analysis shows that a 50-minute delay in start times leads to a 0.15 standard
deviation increase in course grades across the day. This effect comes not only from
improved performance in a student’s earliest class, but also from improved performance
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World of Labor
Evidence-based policy making
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Evidence-based policy making
in classes throughout the day. Despite the fact that students at the Air Force Academy are
not average adolescents (they were high achievers in high school and self-selected into a
military academy), there is no reason to believe that this group of students would be more
adversely affected by early start times than the average adolescent.
Who benets the most from start time changes?
Students across the entire ability distribution experience the benets of later school start
times, including the high-achieving students at the US Air Force Academy. Thus, delaying
start times has the potential to make all students better off. However, certain students
benet more than others. Both the North Carolina and Air Force Academy studies nd
that the benets of later start times are largest for students at the bottom of the grade
distribution [1], [11]. Figure 2 shows how the effect of a one-hour delay in start times
differs across the grade distribution at middle schools in Wake County, North Carolina.
For instance, students in the 30th percentile of the ability distribution end up performing
about three percentile points higher on the mathematics exam as a result of a one-hour
delay in start time, while students at the 90th percentile perform around one percentile
point higher. The fact that benets differ across ability groups allows for opportunities
to alter class schedules for some students if delaying the overall start time is not feasible.
Figure 1. The distribution of grades across school start times shows that the later the
start time, the higher the distribution
0.5
0.4
0.3
0.2
0.1
0
Kernel density
−4−20
Normalized grade
2
7.00 a.m.
7.30 a.m.
7.50 a.m.
4
Note: Grades are “normalized” when certain procedures transform raw grades into standardized ones with an average
at 0 and a standard deviation of 1. This kernel density plot shows the smoothed distribution of normalized course
grades across start times at the US Air Force Academy.
Source: Carrell, S. E., T. Maghakian, and J. E. West. “A’s from zzzz’s? The causal effect of school start time on the
academic achievement of adolescents.” American Economic Journal: Economic Policy 3:3 (2011): 62–81 [11].
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World of Labor
Evidence-based policy making
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Evidence-based policy making
For example, for schools that have free periods as part of the daily schedule, the lower
ability students could be given the rst period off, allowing them to start their day later
than their peers. Alternatively, their schedules could be set up so that they take their less
rigorous classes early in the morning.
How large are the benets?
The benets of later school start times are quite large, especially when compared with
other—more costly—educational interventions. A one-hour delay in a school’s start time
has the same effect as being in a class with one-third fewer students or replacing an
average teacher with one in the 84th percentile of effectiveness.
Figure 2. Students at the lower end of the performance distribution benefit more than
others from a one-hour delay in school start times
Note: Each point in the figure represents the effect of a one-hour later start time in Wake Country, North Carolina,
middle schools for students in different quantiles of the ability distribution on their percentile rank on end of grade
exams. The shaded areas represent 95% confidence intervals. The solid horizontal line is the average effect for all
students, and the dotted horizontal lines bound a 95% confidence interval around the estimated average.
Source: Edwards, F. “Early to rise? The effect of daily start times on academic performance.” Economics of Education
Review 31:6 (2012): 970–983 [1].
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Change in percentile rank
0.20.4
(a) Mathematics
(b) Reading
Ability quantiles
0.60.8
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Change in percentile rank
0.20.4
Ability quantiles
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World of Labor
Evidence-based policy making
World of Labor
Evidence-based policy making
Delaying start times by one hour for students in secondary school would increase overall
student achievement by roughly 0.10 standard deviation, on average. As in previous
studies, this gain can be quantied as a dollar value in order to compare the benets of
this policy change with its potential costs [12]. A one standard deviation rise in test scores
is estimated to increase future earnings by 8%. Assuming a 1% growth rate for real wages
and productivity and a 4% discount rate, this translates to an approximately $10,000
increase in future earnings per student, on average, in present value terms. The benet is
even larger for students at the bottom of the grade distribution.
Channels of impact and optimal start times
There are at least two channels linking later school start times to improved academic
outcomes. The rst has to do with sleep and time of day. Early start times lead to increased
sleep deprivation, which affects students throughout the day. Because adolescents do not
become tired until around 11.00 p.m. or midnight, they are unable to fall asleep early
enough to get the recommended amount of sleep. In addition, regardless of the duration
of sleep, there are times of day when individuals are more alert and capable of learning.
Later start times not only increase the duration of sleep, but they also align more of a
student’s classes with the hours in the day when students are best able to learn.
A second channel through which later start times can boost academic outcomes is
through improved attendance in the rst classes of the day. At many schools, attendance
is lower in early classes, and the later the start time, the higher the attendance in rst-
period classes [7]. However, class attendance is mandatory at the US Air Force Academy,
which implies that the negative effects of early school start times are not driven solely by
absences or tardiness.
While research has established that later start times can improve academic outcomes, no
study has determined the optimal school start time. Studies show that between 7.00 a.m.
and 8.45 a.m., later is better. However, whether students would benet more from having
school start even later, 9.30 a.m. for instance, has not been studied. The randomized
scheduling at the US Air Force Academy provides the best opportunity to shed some light
on this problem. The Air Force Academy study assessed how student performance differs
across class periods relative to rst period, holding all else constant [11]. As shown in
Figure 3, the biggest gains would come from delaying start times to what is traditionally
second or third period in many secondary schools (approximately 8.30–9.30 a.m.). In
the US, most secondary schools start between 7.00 a.m. and 8.30 a.m., with a majority
starting at 7.30 a.m. While there are clear gains to delaying start time to 8.00 a.m. or
later, even small delays in the hour between 7.00 a.m. and 8.00 a.m. have been shown to
increase achievement.
The costs of delaying school start times
Delaying start times, while far more cost-effective than many other education policies
aimed at improving student achievement, is not costless. The two most costly changes,
for instance in the US, that may be needed to accommodate delayed school start times
would be a larger bus eet and costs associated with moving after-school activities to
later in the day: for example, outdoor lighting for athletic elds. While not insubstantial,
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World of Labor
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Evidence-based policy making
the investment seems worthwhile given the large benets for students of later start times.
For schools without bussing systems and those able to accommodate extracurricular
activities in other ways, the cost of this policy change can be even smaller.
To put the estimated costs discussed below in context, recall that delaying start times by
one hour would result in an estimated 0.10 standard deviation increase in overall student
achievement and an approximately $10,000 average increase in future earnings per
student, in present value terms. In the US, the largest cost of delaying start times comes
from altering bussing schedules for schools or districts that operate buses. Many districts
stagger the start times of their three levels of schools—elementary, middle, and high—to
use one set of buses for all schools. Generally, the high schools start rst because of
safety concerns arising from having younger children waiting outside for buses or walking
to school very early in the morning, when it is still dark during much of the school year.
Schools that currently provide bussing for their students and that want to change their high
school start times will have to accommodate the change by having the other school levels
start earlier (at no additional operating cost) or by operating more buses, at additional
cost, so that all schools can start later in the morning. Having districts alter their bussing
system so that all students start school at the same time would cost approximately $150
per student per year—or $1,950 over a student’s school career [10].
Another cost of later start times is the reduction in time available for after-school activities,
such as athletic team practice. The average length of the US school day is 6.6 hours, so a
9.00 a.m. start time, for example, would coincide with a dismissal time of about 3.30 p.m.
Figure 3. Changes in grades across the school day suggest that later start times would boost
achievement for secondary school students
Note: The figure shows the standard deviation change in academic performance in each period relative to the first
period, controlling for the characteristics of the class, students, and their daily schedule. The bars represent the 90%
confidence intervals of the estimate.
Source: Calculations based on US Air Force Academy data.
0.4
0.3
0.2
0.1
0
12
Period
Change in academic
performance relative to period 1
34567
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The educational effects of school start times
World of Labor
Evidence-based policy making
World of Labor
Evidence-based policy making
Many athletic coaches in US schools oppose later school start times because it would
limit the number of daylight hours available for team practices and matches. This is less
of a problem for indoor sports and other activities.
Schools have several options to offset this concern. One option is to install lights on
athletic elds so that students can practice later in the day. The estimated cost of adding
lights to athletic elds would be a one-time expense of approximately $110,000 and an
annual operating cost of $2,500 [12]. The second option is to alter students’ schedules so
that the last period of the day is made available for practice if they are on a sports team
that practices outdoors. Finally, practices and extracurricular activities can be moved to
the morning. While this would not allow students to get more sleep, it would better align
class times with the times of day that students learn best.
LIMITATIONS AND GAPS
One limitation of the literature on later school start times is that it has been unable
to distinguish how much of the benets of later school start times arise from absolute
learning (how much someone has learned) and how much from relative learning (how
much someone has learned compared to their peers). For example, the measured effects
of start time on course grades in the US Air Force Academy study are determined by
the performance of students who have early start times relative to students taking the
same course who start later and have a start time that is more conducive to learning
and potentially allows them to get more sleep [11]. Because not all students at the Air
Force Academy begin class at the same time, the study could not determine the effect of
all students having an earlier or later start time. The effect the study measures is relative
learning. Similarly, the North Carolina study looked at percentile scores on standardized
tests as an outcome, which, by construction, are relative to peers’ test scores in the same
year. In that setting, students’ percentile scores may increase as a result of later start times
not only because of more sleep and increased learning in the classroom, but also because
the test is taken at a time when students perform better.
SUMMARY AND POLICY ADVICE
Secondary school students have been subject to school start times and schedules
developed around the convenience of others, extracurricular activities, and the status
quo, and not around their own best interests. Because adolescents have different internal
clocks and sleep patterns than younger children and adults, early school start times are
not conducive to their learning. Empirical studies of the impact of later start times on
adolescents nd sizable gains in grades and test scores. A one-hour delay in school start
times leads to a 0.10 standard deviation increase in achievement (the same as improving
from a grade of B to a B+ on an A to F scale) in classes throughout the entire day. Scholars
across disciplines agree that adolescents would benet from later school start times. A
growing body of research outside of economics has found that delaying school start times
has positive effects on a number of non-academic outcomes as well, including hours of
sleep, attendance rates, mental health, and frequency of automobile accidents [13].
While research on sleep patterns across the world shows a linear trend toward later
school-night bedtimes from age 11 to age 18 [3], sleep research also shows that the
biological shift toward later time preference during adolescence usually shifts back in
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Evidence-based policy making
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Evidence-based policy making
Competing interests
The IZA World of Labor project is committed to the IZA Guiding Principles of Research Integrity.
The author declares to have observed these principles.
© Teny Maghakian Shapiro
one’s early 20s. This pattern was also detected empirically in the study of Wake County
middle schools, which nds that the benets of later school start times increase with
students’ age [1]. Thus, the policy discussion about later start times should focus rst on
high schools and then on middle schools, but does not apply to elementary schools.
These ndings suggest that schools and districts have an opportunity to improve student
learning and achievement by delaying middle and high school start times. Every school and
district will face its own set of challenges associated with changing start times. Schools
that do not provide bussing, have a dedicated set of buses for high school students, or
already have lighted athletic elds will face the lowest associated costs. A pilot study can
be a useful tool for schools and districts to assess the impact of the schedule change on
their students. Districts with multiple high schools may choose to have one of the schools
start later, while districts with one high school can institute a split schedule in which one
set of students starts (and ends) the school day later.
For schools that are unable to delay start times, changing the conguration of the school
schedule may also improve student outcomes. Research suggests that the benets from
later start times come not only from allowing students to get more sleep, but also from
having classes that are better aligned with the time of day when students are best able
to learn. Better alignment can also be achieved by scheduling extra-curricular activities,
electives, and non-academic classes (such as physical education) at the start of the
school day.
One of the biggest challenges to changing start times is measuring the impact of the change.
Course grades at most schools are subjective, curved (assigned to yield a pre-determined
distribution of grades), and not comparable across years or instructors. Standardized
tests do not necessarily measure what students have learned, most obviously for subjects
not tested and especially for students at the top of the grade distribution. Because of
these issues, school districts need to be thorough in their assessment of the effects of
later start times. Both quantitative measures of achievement (uncurved course grades,
standardized test scores) and qualitative measures (feedback from students and teachers)
should be assessed to get a complete picture of the impacts.
Acknowledgments
The author thanks an anonymous referee and the IZA World of Labor editors for many
helpful suggestions on earlier drafts. The author also thanks Scott Carrell, Kevin Williams,
and Jim West for their contribution to work on this topic. The views expressed in this
article are those of the author and do not necessarily reect the ofcial policy or position
of the US Air Force, the Department of Defense, or the US government.
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REFERENCES
Further reading
Cardinali, D. P. “Chronoeducation: How the biological clock inuences the learning process.”
In: Battro, A. M., K. W. Fischer, and P. J. Léna (eds). The Educated Brain: Essays in Neuroeducation.
Cambridge, UK: Cambridge University Press, 2008; pp. 110–126.
National Sleep Foundation. Sleep in America Poll, Teens and Sleep: Highlights and Key Findings. Arlington,
VA: National Sleep Foundation, 2006.
Key references
[1] Edwards, F. “Early to rise? The effect of daily start times on academic performance.” Economics
of Education Review 31:6 (2012): 970–983.
[2] Crowley, S. J., C. Acebo, and M. A. Carskadon. “Sleep, circadian rhythms, and delayed phase in
adolescents.” Sleep Medicine 8:6 (2007): 602–612.
[3] Gradisar, M., G. Gardner, and H. Dohnt. “Recent worldwide sleep patterns and problems
during adolescence: A review and meta-analysis of age, region, and sleep.”Sleep medicine12:2
(2011): 110 –118 .
[4] Wolfson, A. R., and M. A. Carskadon. “Understanding adolescent’s sleep patterns and school
performance: A critical appraisal.” Sleep Medicine Reviews 7:6 (2003): 491–506.
[5] Goldstein, D., C. Hahn, L. Hasher, U. Wiprzycka, and P. D. Zelazo. “Time of day, intellectual
performance, and behavioral problems in morning versus evening type adolescents: Is there a
synchrony effect?” Personality and Individual Differences 42:3 (2007): 431–440.
[6] Dills, A. K., and R. Hernandez-Julian. “Course scheduling and academic performance.”
Economics of Education Review 27:6 (2008): 646–654.
[7] Cortes, K. E., J. Bricker, and C. Rohlfs. “The role of specic subjects in education production
functions: Evidence from morning classes in Chicago public high schools.”The BE Journal of
Economic Analysis & Policy12:1 (2012).
[8] Wahlstrom, K. “Changing times: Findings from the rst longitudinal study of later high school
start times.” NASSP Bulletin 86:633 (2002): 3–21.
[9] Hinrichs, P. “When the bell tolls: The effect of school starting times on academic achievement.”
Education Finance and Policy 6:4 (2011): 486–507.
[10] Koenig, K. A., M. C. Frey, and D. K. Detterman. “ACT and general cognitive ability.”
Intelligence36:2 (2008): 153–160.
[11] Carrell, S. E., T. Maghakian, and J. E. West. “A’s from zzzz’s? The causal effect of school start
time on the academic achievement of adolescents.” American Economic Journal: Economic Policy 3:3
(2011): 62–81.
[12] Jacob, B. A., and J. E. Rockoff.Organizing Schools to Improve Student Achievement: Start Times, Grade
Congurations, and Teacher Assignments. Washington, DC: Brookings Institution Hamilton Project,
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[13] Wahlstrom, K., B. Dretzke, M. Gordon, K. Peterson, K. Edwards, and J. Gdula. Examining the
Impact of Later School Start Times on the Health and Academic Performance of High School Students:
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Educational Improvement, 2014.
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