later school start times

A large study in middle and high school students looked at the impact of later school start times on teens’ sleep patterns and schoolwork.

It’s well known that getting a good night’s sleep is essential for health. This is especially important for teenagers, who are still growing physically and mentally. However, some changes in adolescence, such as adjustments in the body’s internal clock and the onset of puberty, can disrupt sleep. When this is combined with social pressures and the need to get up early for school, many teens are not getting enough sleep. The American Academy of Sleep Medicine recommends that middle and high schools should start at 8.30 am or later to support teen health. However, the US Centers for Disease Control found that only around 14% of high schools and 19% of middle schools are in line with this advice.

Many teens do not get enough sleep

Researchers in Colorado conducted a large study that included middle and high school students, to look at the impact of later school start times on students sleep, schoolwork, and extracurricular activities. They recently reported their findings in the journal Sleep, and at the 33rd Annual Meeting of the Associated Professional Sleep Societies, (June 12, 2019, San Antonio, USA).

In the autumn of 2017, a school district in Denver, Colorado (USA), delayed school start times for middle school students by 50 mins (8.00 am to 8.50 am) and for high school students by 70 mins (7.10 am to 8.20 am). The study looked at the impact of the later school start times on over 15,000, Grade 6 to 11 students, who completed online surveys before (Spring 2017, n=15,700) and after the start time changes (Spring 2018, n=18,607). The survey asked about weekday and weekend bedtimes, wake times and total sleep times, sleepiness during homework, and academic engagement (a measure of participation in school activities).

Later school start times had several benefits for teens’ sleep and schoolwork

Following later school start times, sleep on school nights was 31 mins longer in middle school students and 48 mins longer in high school students. Weekend oversleep (sleep catch-up) was reduced by 38 mins in middle school students and by 59 mins in high school students. Significantly more students obtained sufficient sleep (middle school ≥ 9 hrs, 38% vs 44%; high school ≥ 8 hrs, 27% vs 58%). The percentage of students who reported feeling too sleepy to do homework was lower after the later school start times (middle school students, from 46% to 35%; high school students, from 71% to 56%). Scores on a measure of academic engagement were significantly higher after the start-time change for both middle and high school students. Overall, there was a minimal decrease in extracurricular participation.

“This study provides additional support that delaying middle and high school start times results in increased sleep duration for adolescents due to later wake times,” said Dr. Lisa Meltzer, the principal investigator. Dr. Scott Siegfried, School District Superintendent in the school areas studied, received positive feedback from students taking part. “That extra sleep makes a real difference in terms of health and wellness,” said Dr. Siegfried, “The change in our start times has been a positive step and benefited our students’ everyday routines.”

Written by Julie McShane, MA MB BS


  1. Meltzer LJ, McNally J, Wahlstrom KL, et al. Impact of changing middle and high school start times on sleep, extracurricular activities, homework and academic engagement. Sleep 2019; 42(Suppl 1):A328-A329.
  2. American Academy of Sleep, Press Release, 7 June 2019. “Teens sleep longer, are more alert for homework when school starts later.”

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