School start time delays and high school educational outcomes: Evidence from the START/LEARN study

Introduction: Delaying high school start times extends adolescents' nightly sleep, but it is less clear how it affects educational outcomes. We expect links between school start time delays and academic performance because getting enough sleep is a key input to the cognitive, health, and behavioral factors necessary for educational success. Thus, we evaluated how educational outcomes changed in the 2 years following a school start time delay. Methods: We analyzed 2153 adolescents (51% male, 49% female; mean age 15 at baseline) from START/LEARN, a cohort study of high school students in the Minneapolis—St. Paul, MN, USA metropolitan area. Adolescents experienced either a school start time delay (“policy change schools”) or consistently early school start times (“comparison schools”). We compared patterns of late arrivals, absences, behavior referrals, and grade point average (GPA) 1 year before (baseline, 2015–2016) and 2 years after (follow-up 1, 2016–2017 and follow-up 2, 2017–2018) the policy change using a difference-in-differences analysis. Results: A school start time delay of 50–65 min led to three fewer late arrivals, one fewer absence, a 14% lower probability of behavior referral, and 0.07–0.17 higher GPA in policy change schools versus comparison schools. Effects were larger in the 2nd year of follow-up than in the 1st year of follow-up, and differences in absences and GPA emerged in the second year of follow-up only. Conclusions: Delaying high school start times is a promising policy intervention not only for improving sleep and health but for improving adolescents' performance in school.