A quasi-experimental study of the impact of school start time changes on adolescents' mood, self-regulation, safety, and health.

Objective: To determine whether school start time changes impact adolescents' mood, self-regulation, safety, and health.

Methods: In September 2015, two school start time changes were implemented in Fairfax County (VA) Public Schools: a 50-minute delay (to 8:10 am) for high schools and secondary schools and a 30-minute advance (to 7:30 am) for middle schools. We conducted cross-sectional surveys of students' sleep, mood, self-regulation, health, and safety before (2017 students) and after (1180 students) these changes.

Results: Adjusted for confounders, a 50-minute delay was associated with a decreased prevalence of low mood (-4.7%; 95% confidence interval [CI]: -8.2%, -1.2%), drowsy driving, (-8.4%; 95% CI: -15.9%, -0.9%), and skipping breakfast (-4.2%; 95% CI: -8.1%, -0.2%) but no other significant changes. There were no significant changes associated with a 30-minute advance.

Conclusions: A 50-minute delay in school start time in high schools and secondary schools was associated with a decreased prevalence of low mood, drowsy driving, and skipping breakfast. A 30-minute advance in start time in middle schools was not associated with any appreciable changes.