Later middle and high school start times

Evidence Rating  
Evidence rating: Scientifically Supported

Strategies with this rating are most likely to make a difference. These strategies have been tested in many robust studies with consistently positive results.

Disparity Rating  
Disparity rating: Inconclusive impact on disparities

Strategies with this rating do not have enough evidence to assess potential impact on disparities.

Health Factors  
Date last updated

Start times for middle and high schools are often at or before 8 a.m.1, but can be delayed via policy change, often at the school or district level. Insufficient sleep is common among U.S. adolescents and is associated with higher risks for health problems such as poor mental health, type 2 diabetes, and injuries2. Delaying school start times until 8:30 a.m. or later can provide an opportunity for students to get the recommended 8-10 hours of sleep2, 3. Biological sleep-wake cycles, or circadian rhythms, shift up to two hours later for adolescents at the onset of puberty4.

What could this strategy improve?

Expected Benefits

Our evidence rating is based on the likelihood of achieving these outcomes:

  • Increased sleep

Potential Benefits

Our evidence rating is not based on these outcomes, but these benefits may also be possible:

  • Improved mental health

  • Increased academic achievement

  • Reduced motor vehicle crashes

  • Improved student attendance

  • Improved on-task behavior

What does the research say about effectiveness?

There is strong evidence that middle and high school start times of 8:30 a.m. or later increase sleep3, 5, 6, 7.

Later middle and high school start times increase sleep primarily by delaying student wake times8 and can decrease clinically significant daytime sleepiness9. Insufficient sleep is associated with increased depression, anxiety, anger, and negative affect in adolescents; sufficient sleep contributes to optimal mood and the ability to regulate emotions10. Later school start times also appear to improve mental health for adolescents3, 5, such as reducing depression symptoms3 and increasing psychological wellbeing11. However, later school start times may reduce depression more for students from high income families than students from low income families12.

While later school start times appear to have some positive effects on grades and test scores, their overall impact remains unclear and additional stronger studies are needed13, 14. Rigorous evaluation of these effects remains challenging since class grades are not standardized, and some standardized tests (e.g., SATs and ACTs) are not taken by all students15.

Delayed school start times appear to improve concentration and ability to pay attention in class15, 16 and can decrease late arrivals, absences, and behavior referrals17, 18. Later school start times have minimal to no impacts on extracurricular participation and employment for high school students19 and may also increase graduation rates18, 20.

Overall, areas with later school start times appear to have lower teen vehicle crash rates than areas with earlier school start times3, 15, 21, 22, though in one Kansas-based study later school start times decreased evening teen crash rates but increased morning accidents23. Later school start times for high school students may also increase healthy eating behaviors such as eating breakfast and having supper with their family24.

Districts that successfully implement a later school start time have strong leadership, educate their families and community members, address concerns early while building consensus around action8, 25, 26, and implement new transportation policies, such as a “flipped bussing” approach where elementary schools begin before middle and high schools8. The cost of changing bus schedules is frequently cited as an obstacle to later school start times, but some districts have realized savings in transportation costs after delaying start times15. Including education about the importance of sleep while implementing a delayed school start time may increase the number of students getting more sleep and maintain initial increases over the long-term4, 27.

Earlier start times for elementary schools slightly decrease sleep duration for elementary students but do not increase daytime sleepiness9, 28 and do not have significant impacts on academic outcomes28. Experts suggest that elementary students can start school earlier than middle or high schools if staggered bus schedules are needed9, 28. Later school start times can also benefit middle and high school teachers and parents by increasing sleep and improving daytime functioning, with minimal impacts on elementary school teachers and parents29, 30.

How could this strategy advance health equity? This strategy is rated inconclusive impact on disparities.

It is unclear what impact later middle and high school start times could have on disparities in adolescent sleep across populations. Students who are female, Black, or Asian are more likely to get less sleep than those who are male, white, or Hispanic35, and students who are from families with lower incomes have poorer and less consistent sleep than those from families with higher incomes36. Available evidence suggests later school start times may benefit female students’ sleep more, narrowing sleep disparities between males and females37. However, international evidence suggests later school start times may result in larger improvements in sleep for students at private schools more than students at public schools5.

Students who are economically disadvantaged, Hispanic, Black, or Native American graduate from high school at lower rates than students who are not economically disadvantaged, white, or Asian38, 39. While later school start times can increase graduation rates for all groups, there may be a several year delay following implementation before graduation rates for students from low income families and students who are Black improve20. A North Carolina-based study suggests that delaying school start times may temporarily increase absences, which disproportionately impact students of color, students from low income families, and students who are not doing well academically7. Students from disadvantaged backgrounds may be more likely to benefit academically from later school start times40, 41, 42.

What is the relevant historical background?

In the 1990s, researchers established that teenagers have biologically driven sleep and wake patterns that are different from young children or adults43. Recent surveys show that six in ten middle school students and seven in ten high school students did not get enough sleep on school nights2.

Equity Considerations
  • What time do schools start in your school district? How do these start times affect students, families, and community members differently?
  • What concerns do community members have about school start times?
  • How can you share information about the importance of sleep for everyone, and especially adolescents?
  • What funding and resources are available to implement later school start times? Are there opportunities for cost savings?
Implementation Examples

According to the 2017-2018 National Teacher and Principal Survey (NTPS), 17% of high schools start at 8:30 a.m. or later1. Average high school start times vary across states; Alaska, Iowa, Minnesota, South Carolina are states with average start times after 8:15 a.m.1. In 2019, California passed SB 328 which mandates middle schools must start no earlier than 8:00 a.m. and high schools must start no earlier than 8:30 a.m.31. Florida passed HB 733, which also requires later school start times to be implemented by the 2026-2027 school year32. As of 2023, bills related to school start times have been introduced in at least 26 states and territories33.

The federal ZZZ’s to A’s Act (HR 8787), first introduced in 1997, was again introduced in 2022. If presented to Congress and passed into law, the Act would direct the Secretary of Education to conduct a study examining the relationship between SSTs and adolescent health, well-being, and academic performance34.

Implementation Resources

Resources with a focus on equity.

SSL - Start School Later.


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1 NCES-School start - U.S. Department of Education (U.S. ED), Institute of Educational Sciences (IES), National Center for Education Statistics (NCES). Start time for U.S. public high schools.

2 CDC-Sleep and health - Centers for Disease Control and Prevention (CDC). Sleep and health.

3 Morgenthaler 2016 - Morgenthaler TI, Hashmi S, Croft JB, et al. High school start times and the impact on high school students: What we know, and what we hope to learn. Journal of Clinical Sleep Medicine. 2016;12(12):1681-1689.

4 Au 2014 - Au R. School start times for adolescents. Pediatrics. 2014;134(3):642-649.

5 Yip 2022 - Yip T, Wang Y, Xie M, et al. School start times, sleep, and youth outcomes: A meta-analysis. Pediatrics. 2022;149(6):e2021054068.

6 Bowers 2017 - Bowers JM, Moyer A. Effects of school start time on students’ sleep duration, daytime sleepiness, and attendance: A meta-analysis. Sleep Health. 2017;3(6):423-431.

7 Fuller 2024 - Fuller SC, Bastian KC. Saved by the bell schedule? The effects of a later school start time on high schoolers in an urban district. Urban Education. 2024;59(5):1552-1585.

8 Mousavi 2023 - Mousavi Z, Troxel WM. Later school start times as a public health intervention to promote sleep health in adolescents. Current Sleep Medicine Reports. 2023;9:152-160.

9 Meltzer 2021 - Meltzer LJ, Wahlstrom KL, Plog AE, Strand MJ. Changing school start times: Impact on sleep in primary and secondary school students. Sleep. 2021;44(7):1-14.

10 Short 2020 - Short MA, Booth SA, Omar O, Ostlundh L, Arora T. The relationship between sleep duration and mood in adolescents: A systematic review and meta-analysis. Sleep Medicine Reviews. 2020;52:101311.

11 Berger 2018 - Berger AT, Widome R, Troxel WM. School start time and psychological health in adolescents. Current Sleep Medicine Reports. 2018;4:110-117.

12 Peltz 2022 - Peltz JS, Buckhalt JA. Equal Benefits? An examination of the potential consequences of later school start times for adolescents and their mental health. Journal of School Health. 2022;92(3):309-315.

13 Biller 2022 - Biller AM, Meissner K, Winnebeck EC, Zerbini G. School start times and academic achievement - A systematic review on grades and test scores. Sleep Medicine Reviews. 2022;61:101582.

14 Campbell-Marx 2017 - Marx R, Tanner-Smith EE, Davison CM, et al. Later school start times for supporting the education, health and well-being of high school students. Campbell Systematic Reviews. 2017.

15 Wheaton 2016 - Wheaton AG, Chapman DP, Croft JB. School start times, sleep, behavioral, health, and academic outcomes: A review of the literature. Journal of School Health. 2016;86(5):363-381.

16 Minges 2016 - Minges KE, Redeker NS. Delayed school start times and adolescent sleep: A systematic review of the experimental evidence. Sleep Medicine Reviews. 2016;28:82-91.

17 James 2023 - James SA, Erickson DJ, Lammert S, Widome R. School start time delays and high school educational outcomes: Evidence from the START/LEARN study. Journal of Adolescence. 2023;95(4):751-763.

18 Lenard 2020 - Lenard M, Morrill MS, Westall J. High school start times and student achievement: Looking beyond test scores. Economics of Education Review. 2020;76:101975.

19 Meltzer 2022 - Meltzer LJ, Plog AE, Wahlstrom KL, McNally J. Changing school start times: Impact on extracurricular activities and employment. Frontiers in Sleep. 2022;1:1044457.

20 McKeever 2022 - McKeever PM, Dodd R, O’Sullivan DM. Delayed high school start times and graduation and attendance rates over 4 years: The impact of race and socioeconomics. Journal of Clinical Sleep Medicine. 2022;18(11):2537-2543.

21 Bin-Hasan 2020 - Bin-Hasan S, Kapur K, Rakesh K, Owens J. School start time change and motor vehicle crashes in adolescent drivers. Journal of Clinical Sleep Medicine. 2020;16(3):371-376.

22 Foss 2019 - Foss RD, Smith RL, O’Brien NP. School start times and teenage driver motor vehicle crashes. Accident Analysis and Prevention. 2019;126:54-63.

23 Bostwick 2018 - Bostwick VK. Saved by the morning bell: School start time and teen car accidents. Contemporary Economic Policy. 2018;36(4):591-606.

24 Widome 2023 - Widome R, Erickson DJ, Laska MN, et al. Impact of delaying high school start times on weight and related behaviors - the START study. Preventive Medicine. 2023;172:107548.

25 Fitzpatrick 2021 - Fitzpatrick JM, Silva GE, Vana KD. Perceived barriers and facilitating factors in implementing delayed school start times to improve adolescent sleep patterns. Journal of School Health. 2021;91(2):94-101.

26 Owens 2014 - Owens J, Drobnich D, Baylor A, Lewin D. School start time change: An in-depth examination of school districts in the United States. Mind, Brain, and Education. 2014;8(4):182-213.

27 Thacher 2016 - Thacher PV, Onyper SV. Longitudinal outcomes of start time delay on sleep, behavior, and achievement in high school. SLEEP. 2016;39(2):271-281.

28 Bastian 2023 - Bastian KC, Fuller SC. Early birds in elementary school? School start times and outcomes for younger students. Educational Evaluation and Policy Analysis. 2023;45(3):399-421.

29 Wahlstrom 2023 - Wahlstrom KL, Plog AE, McNally J, Meltzer LJ. Impact of changing school start times on teacher sleep health and daytime functioning. Journal of School Health. 2023;93(2):128-134.

30 Meltzer 2022a - Meltzer LJ, Wahlstrom KL, Plog AE, McNally J. Impact of changing school start times on parent sleep. Sleep Health. 2022;8(1):130-134.

31 CA-SB328 - California State Legislature. 2021-2022 Legislative Session. Senate Bill 328: Local education agencies: Before and after school programs: Middle school and high school start time.

32 FL-HB733 - Florida State Legislature. House Bill 733: Middle school and high school start times.

33 SSL-Legislation - Start School Later. Legislation.

34 HR 8787 - 117th Congress 2021-2022. House of Representatives (HR) 8787: ZZZ’s to A’s Act.

35 CDC MMWR-Wheaton 2016 - Wheaton AG, Jones SE, Cooper AC, Croft JB. Short sleep duration among middle school and high school students — United States, 2015. Morbidity and Mortality Weekly Report (MMWR). 2018;67(3):85-90.

36 Marco 2011 - Marco CA, Wolfson AR, Sparling M, Azuaje A. Family socioeconomic status and sleep patterns of young adolescents. Behavioral Sleep Medicine. 2011;10(1):70-80.

37 Groen 2019 - Groen JA, Pabilonia SW. Snooze or lose: High school start times and academic achievement. Economics of Education Review. 2019;72:204-218.

38 NCES-Young adult education - U.S. Department of Education (U.S. ED), Institute of Educational Sciences (IES), National Center for Education Statistics (NCES). Educational attainment of young adults.

39 NCES-HS graduation rates - U.S. Department of Education (U.S. ED), Institute of Educational Sciences (IES), National Center for Education Statistics (NCES). High school graduation rates.

40 Bastian 2018a - Bastian KC, Fuller SC. Answering the bell: High school start times and student academic outcomes. AERA Open. 2018;4(4):1-12.

41 Brookings-Jacob 2011 - Jacob BA, Rockoff JE. Organizing schools to improve student achievement: Start times, grade configurations, and teacher assignments. Brookings Institution, Hamilton Project. 2011.

42 Edwards 2012 - Edwards F. Early to rise? The effect of daily start times on academic performance. Economics of Education Review. 2012;31(6):970-983.

43 Wahlstrom 2002 - Wahlstrom K. Changing times: Findings from the first longitudinal study of later high school start times. NASSP Bulletin. 2002;86(633):3-21.