A’s from Zzzz’s? The Causal Effect of School Start Time on the Academic Achievement of Adolescents

The US Air Force decided to do a rigorous study on the relationship between the start of the school day and academic success for their first year cadets. Because all cadets pursued the same curriculum and lived on campus, they were able to control the timing and amount of sleep of their cadets and compare academic success on fairly equal ground.

This paper identifes the causal effect of school start time on the academic achievement of adolescents. To do so, we use data from the United States Air Force Academy (USAFA) to take advantage of the randomized assignment of students to courses and instructors, as well as two policy changes in the school start time over a three-year period. Random assignment, mandatory attendance, along with extensive background data on students, allow us to examine how school start time affects student achievement without worrying about confounding factors or self- selection issues that bias existing estimates. USAFA’s grading structure for core courses allows for a consistent measure of student achievement; faculty members teaching the same course in each semester use an identical syllabus, give the same exams during a common testing period, and assign course grades jointly with other instructors, allowing for standardized grades within a course-semester.

Their findings: students who slept 50 minutes later saw an academic improvement equivalent to raising teacher quality by one standard deviation. That would be a substantially better teacher. Other researchers have put these in terms we might understand: the effect was equivalent to reducing class size by one third.

We find that early school start times negatively affect student achievement—students randomly assigned to a first period course earn lower overall grades in their classes on the same schedule day compared to students who are not assigned a first period class on that day. We verify that this negative effect is not solely a result of poor performance during first period courses. Although students perform worse in first period classes compared to other periods, those with first period classes also perform worse in their subsequent classes on that schedule day. These estimates are robust to professor by year by M/T day fixed effects and individual student fixed effects.

Our findings have important implications for education policy; administrators aiming to improve student achievement should consider the potential benefits of delaying school start time. A later start time of 50 minutes in our sample has the equivalent benefit as raising teacher quality by roughly one standard deviation. Hence, later start times may be a cost-effective way to improve student outcomes for adolescents.

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