Later middle and high school start times

Evidence Rating  
Evidence rating: Some Evidence

Strategies with this rating are likely to work, but further research is needed to confirm effects. These strategies have been tested more than once and results trend positive overall.

Health Factors  
Date last updated

Start times for middle and high schools are typically very early, often before 8 a.m., but can be delayed via policy change, often at the school or district level. Insufficient sleep is common among U.S. adolescents; delaying school start times substantially, until after 8:30 or 9:00 a.m., can provide an opportunity for students to get the recommended 8.5-9.5 hours of sleep on school nights1, 2. Biological sleep-wake cycles, or circadian rhythms, shift up to two hours later for adolescents at the onset of puberty3.

What could this strategy improve?

Expected Benefits

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

  • Improved student attendance

  • Improved on-task behavior

Potential Benefits

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

  • Increased sleep

  • Increased academic achievement

  • Reduced motor vehicle crashes

  • Improved mental health

  • Reduced risky health behaviors

What does the research say about effectiveness?

There is some evidence that delaying school start times (SSTs) for middle and high school students by an hour or more, preferably after 9 am, decreases tardiness, improves attendance, and improves on-task behavior and classroom engagement. Later SSTs have been shown to increase sleep, primarily by delaying rise times, and reduce daytime sleepiness and caffeine use among adolescents2, 4, 5, 6. Insufficient sleep is negatively associated with academic performance in middle school, high school, and college7. Additional evidence, particularly longer term studies, is needed to confirm the effects of delayed start times2.

Later SSTs can improve academic indicators such as grades or state-level test scores6, 8, 9, 10, 11. Delayed SSTs also appear to be associated with improved concentration and ability to pay attention in class4, 5. The academic effects of later SSTs appear to be stronger for students with lower levels of academic achievement and increases in reading and math scores appear larger for disadvantaged students than more advantaged students9, 12. However, 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 students4.

Areas with later school start times have significantly lower teen crash rates than areas with earlier school start times2, 4. Later SSTs may also reduce depression symptoms and improve mood2, 4, 5. Delayed SSTs are a suggested strategy to reduce teen engagement in risky behaviors such as alcohol or drug use and sexual activity1, 4.

Case studies suggest that successful efforts to implement a later SST have strong leadership, community-wide education efforts, consensus building components, and policies to support new transportation and extracurricular activity logistics13. Including education about the importance of sleep while implementing a delayed SST may increase the number of students getting more sleep and maintain initial increases over the long-term3, 14, 15.

The cost of changing bus schedules is frequently cited as an obstacle to later SSTs; however, several school districts have realized savings in transportation costs after delaying start times4. One cost benefit analysis of later SSTs estimates a benefit to cost ratio of 9 to 112.

A Kentucky-based study suggests that early elementary school start times are also associated with poorer academic performance and increased absences. Starting elementary schools earlier to delay SSTs for middle and high schools may not be beneficial16.

Implementation Examples

The Centers for Disease Control and Prevention (CDC) estimate that less than 1 in 5 middle and high schools in the U.S. start at 8:30 am or later1. Most public schools start before 8:30 am. Most schools in Alaska (76%) and North Dakota (78%) start after 8:30 am, and no schools in Hawaii, Mississippi, and Wyoming start after 8:30 am1. As of 2014, at least 70 public school districts, approximately 1,000 schools, have implemented a delayed school start time13; 44 states have shared examples of these successful efforts17

The federal ZZZ’s to A’s Act (HR 1306) was assigned to a congressional committee for consideration in 2015. 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 performance18.

Implementation Resources

CDC-Sleep - Centers for Disease Control and Prevention (CDC). Sleep and sleep disorders.

NSF-School start - National Sleep Foundation (NSF). Backgrounder: Later school start times.


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1 CDC-School start - Centers for Disease Control and Prevention (CDC). Schools start too early: Starting school later can help improve an adolescent’s health, academic performance, and quality of life.

2 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.

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

4 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.

5 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.

6 Brown 2011 - Brown RS, Presley A, Newton L, Davison C. Eastern Commerce Collegiate Institute’s late start: Year one interim report. Toronto: Research and Information Services Department, Toronto School District Board; 2011.

7 Wolfson 2003b - Wolfson AR, Carskadon MA. Understanding adolescents’ sleep patterns and school performance: A critical appraisal. Sleep Medicine Reviews. 2003;7(6):491–506.

8 Carrell 2011 - Carrell SE, Maghakian T, West JE. A’s from Zzzz's? The causal effect of school start time on the academic achievement of adolescents. American Economic Journal: Economic Policy. 2011;3(3):62–81.

9 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.

10 CAREI-Wahlstrom 2014 - Wahlstrom KL, Dretzke BJ, Gordon MF, et al. Examining the impact of later high school start times on the health and academic performance of high school students: A multi-site study. St. Paul, MN: Center for Applied Research and Educational Improvement (CAREI), University of Minnesota (UMN); 2014.

11 Wolfson 2007 - Wolfson AR, Spaulding NL, Dandrow C, Baroni EM. Middle school start times: The importance of a good night’s sleep for young adolescents. Behavioral Sleep Medicine. 2007;5(3):194–209.

12 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.

13 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.

14 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.

15 NSF-School start - National Sleep Foundation (NSF). Backgrounder: Later school start times.

16 Keller 2015 - Keller PS, Smith OA, Gilbert LR, et al. Earlier school start times as a risk factor for poor school performance: An examination of public elementary schools in the Commonwealth of Kentucky. Journal of Educational Psychology. 2015;107(1):236–245.

17 SSL-Success - School Start Later (SSL). Healthy hours: Success stories.

18 GovTrack-HR 1306 - House of Representatives congressional bill H.R. 1306: The ZZZ’s to A's Act.