A new study in SLEEP, published by Oxford University Press, demonstrates the significant benefits of later school start times for middle and high school students’ sleep schedules.

Sleep is essential to a student’s overall health, social development, and academic achievement, yet lack of sleep is common among children and adolescents. Biological changes to sleep cycles during puberty make falling asleep early difficult for adolescents. This, coupled with early school start times, means that students often end up with insufficient sleep.

Approximately 28,000 elementary, middle, and high school students and parents completed surveys annually, before changes to school start times and for two years afterward. Participating elementary schools started 60 minutes earlier, middle, 40-60 minutes later, and high school started 70 minutes later. Student and parent surveys separately asked about students’ typical bedtime and wake time on both weekdays and weekends. The surveys also asked respondents to report on students’ quality of sleep and their experience of daytime sleepiness.

Researchers found that the greatest improvements in these measures occurred for high school students, who obtained an extra 3.8 hours of sleep per week after the later start time was implemented. More than one in ten high school students reported improved sleep quality and one in five reported less daytime sleepiness. The average “weekend oversleep,” or additional sleep on weekends, amongst high schoolers dropped from just over two hours to 1.2 hours, suggesting that with enough weekday sleep, students are no longer clinically sleep deprived and no longer feel compelled to “catch up” on weekends. Likewise, middle school students obtained 2.4 additional hours of sleep per week with a later school start time. Researchers saw a 12% decrease in middle schoolers reporting daytime sleepiness. The percent of elementary school students reporting sufficient sleep duration, poor sleep quality, or daytime sleepiness did not change over the course of the study.

The benefits of later start times were similar across racial and socioeconomic groups, but survey results indicated differences in weekday bedtimes. The authors encourage steps to be taken to “identify and ameliorate systemic factors that contribute to these differences,” recommending education programs developed in partnership with families to ensure that guidance for adjusting bedtimes and increasing sleep opportunities are sensitive to sociocultural and environmental factors.

Previous studies have not concurrently considered the impact of changing start times on sleep for students from Kindergarten through 12th grade, a key factor in policy outcomes due to the need for school districts to stagger start times to accommodate transportation schedules.

“This study is remarkable due to the large sample size, the inclusion of elementary and middle school students, the two-year follow-up, and both student and parent report. It also provides the strongest evidence to date that moving elementary school start times to 8:00 am caused no significant negative effect on student sleep or daytime sleepiness. As students return to in-person learning, it is important for districts to consider healthy start times for all students.”