Delaying high-school start times increases student achievement

Contact | Jackie Kerstetter:, Education Next

Delaying high-school start times increases student achievement
Successful efforts to push back start times offer lessons for other districts

May 16, 2019—Though both the American Academy of Pediatrics and the American Academy of Sleep Medicine recommend starting high school at or after 8:30 a.m., 87 percent of U.S. high schools begin earlier. In a new research article for Education Next, Jennifer Heissel of the Naval Postgraduate School and Samuel Norris of the University of Chicago present findings from the first study to quantify the potential academic benefits of delaying high-school start times. They find that later school start times increase achievement on standardized tests for all students in both math and reading, but that the size of those effects is the most pronounced for adolescents in math.

Heissel and Norris conducted their analyses on students in the Florida Panhandle, where the presence of two time zones creates big differences in school start times relative to sunrise, referred to as “relative start times.” They used student and school data from the Florida Department of Education covering 15 school years, from 1998-99 to 2012-13, tracking individual students’ achievement on the annual Florida Comprehensive Assessment Test in math and reading. The study focuses on students who live near the time-zone boundary and move between time zones either from east to west (increasing sunlight relative to start times) or from west to east (decreasing sunlight relative to start times).

Among the key findings:

Later start times increase math and reading scores. Start times that are one hour later relative to sunrise increase adolescent students’ math scores by 8 percent of a standard deviation—equivalent to about three months of learning—and younger students’ scores by 1 to 2 percent of a standard deviation. In reading, delaying start times by one hour increases scores by 6 percent of a standard deviation for both adolescent and younger students.

Advantages in math spike at puberty. The effects of later school start times on math scores spike for girls at age 11 and for boys at age 13, the average ages at which physiological changes due to puberty delay the onset of sleep and make it more difficult to wake up in the morning. Notably for boys, the size of the effect doubles from 5 to 10 percent of a standard deviation at age 13.

Switching start times benefits older students. Moving elementary and middle school start times earlier and high school later would increase minority student achievement in high school by 6 percent of a standard deviation in math and 8 percent of a standard deviation in reading. For white students, math scores would increase by 6 percent of a standard deviation and reading scores by 2 percent of a standard deviation. The effects for younger students are negative, but small: on average, reading and math scores for ele­mentary and middle-school students would decline by roughly 1 percent of a standard deviation across all student subgroups.

In an accompanying article, journalist Danielle Dreilinger examines three districts in Indiana, Minnesota, and West Virginia that have successfully delayed school start times for high-school students. Dreilinger contrasts their experiences to an unsuccessful 2017 rescheduling attempt in Boston Public Schools to draw five lessons for districts interested in pursuing later high-school start times. Crucial to successful efforts, she says, is to clearly communicate the benefits to students while anticipating and addressing family concerns.

To speak to the authors or receive an embargoed copy of “Rise and Shine: How school start times affect academic performance” by Jennifer Heissel and Samuel Norris or “How to Make School Start Later: Early-morning high school clashes with teenage biology” by Danielle Dreilinger, please contact Jackie Kerstetter at Both articles will be available Tuesday, May 21 on and will appear in the Summer 2019 issue of Education Next, available in print on May 24, 2019.

About the Authors: Jennifer Heissel is an assistant professor at the Graduate School of Business and Public Policy at the Naval Postgraduate School. Samuel Norris is an assistant professor at the Harris School of Public Policy at the University of Chicago. Danielle Dreilinger is a freelance writer based in New Orleans.

About Education Next: Education Next is a scholarly journal committed to careful examination of evidence relating to school reform, published by the Education Next Institute and the Program on Education Policy and Governance at the Harvard Kennedy School. For more information, please visit

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