Biology vs. ecology: a longitudinal examination of sleep, development, and a change in school start times

Secondary school start times are associated with student sleep and daytime functioning; however, no study examining this association has included linked longitudinal data for both primary and secondary students. To understand the interplay between biology (ie, normal developmental changes in sleep) and ecology (ie, school start times), this study examined sleep and daytime functioning in elementary/primary and secondary school students over a three-year period that included changes to school start times.

Students (grades 3-10, n = 6168) and parents (for student grades Kindergarten-2, n = 2772) completed annual surveys before (pre-change) and for two-years after (post-change, follow-up) implementation of new school start times (elementary/primary: 60 min earlier, secondary: 50-80 min later). Participants were 48.9% female, 65.5% White, and 16.2% qualified for free/reduced lunch.

With new school start times, significant changes were found for weekday wake times and sleep duration; elementary/primary students woke earlier (23 min) and obtained less sleep (14 min), while secondary students woke later (44 min) and obtained more sleep (31 min). Small changes in weekend sleep duration (<7 min) were found across levels. Secondary school students had significant improvements in daytime functioning post-change, due in part to changes in sleep duration. Minimal changes in elementary/primary students' daytime functioning was found, despite shorter sleep duration.

School start times are a significant factor in weekday wake times for students across grade levels, while later bedtimes are more a factor of normal development. Later start times positively affected secondary students' daytime functioning, with non-significant findings for earlier elementary/primary start times.