Later School Times, Sharper Minds

Art Scholz, Early Bus (2009)

One hour later, and middle schoolers sleep more and think better (confirmed by an actigraph, not just a survey)

STUDY: Reynaud E et al, Scientific Reports 2026 (Article in Press).

STUDY TYPE: Randomized controlled trial

FUNDING: National Education Scientific Council (France); IDEE Program (ANR-21-ESRE-0034)

Background

Adolescents are biologically wired to fall asleep later, but most schools still open their doors at 8 a.m. That mismatch builds chronic sleep debt across the school week. Chronic sleep loss in adolescents links to daytime sleepiness, attention problems, mood instability, and increased substance use. Delaying school start times has been proposed as the simplest fix, but most previous studies relied on self-report and lacked proper control groups.

The Study

• 73 early adolescents (average age 12.8 years, 66% girls) at a French boarding school, randomized by class to an 8 a.m. start (control) or a 9 a.m. start (delayed), with follow-up at 6 months.
• Sleep measured objectively with wrist actigraphy; daytime sleepiness measured with the French Sleepiness Scale for Adolescents (FSSA); inhibitory control measured with the Stroop task; sustained attention measured with the Sustained Attention to Response Task (SART).
• Primary outcome: total sleep time.

Results

After 6 months, those who started school later slept more: a 26-minute difference: 7 hours 30 minutes vs. 7 hours 4 minutes (effect size 0.93). They woke up later, but there wasn’t a change in when they fell asleep.

Daytime sleepiness rose significantly in the control group but stayed flat in the delayed group (effect size 0.52). On the Stroop task, inhibitory control improved in the delayed group while the control group showed no change (effect size 0.79). The effect on sustained attention trended in the same direction but fell just short of significance.

Evening chronotypes (“night owls”) gained the most: 28.5 additional minutes of sleep compared to 9.6 minutes in morning-type students.

Limitations

• Small actigraphy sample (N = 50), with high dropout partly from control-group boys who stopped wearing the device.
• Study conducted in a boarding school with fixed bedtimes and lights-out rules, limiting generalizability to day schools.
• Blinding was impossible by design.

Practice Implications

1. Early start times make students tired and cognitively impaired.
2. These effect sizes are in the moderate to large range, suggesting the differences would be noticed by a casual observer.
3. Short of policy change, a dawn simulator in morning and blue-light blocking glasses at night can help night owls adjust to these routines.