Adolescents with high school start times (SSTs) at 8:30 am or later, compared with adolescents with earlier SSTs, had significantly longer actigraphy-measured sleep, according to a recent study. These findings support pediatric and public health expert recommendations for SSTs after 8:30 am. 383 adolescents (median [M] age=15.5) participated in the age 15 wave of the Fragile Families & Child Wellbeing Study, a national birth cohort study sampling from 20 large US cities. Multilevel models used daily observations (n=1,116 school days, M days=2.9) of sleep and SSTs from concordant daily diary and actigraphy. A diverse range of SSTs were included in the analyses (M SST=8:08), and were presented in the following categories: before 7:30, 7:30–7:59, 8:00-8:29, and 8:30 or later. Researchers found:

• Adolescents starting school at 8:30 or later exhibited significantly longer actigraphically-assessed 24-hour sleep duration (by 21–34 minutes) and later sleep offset (by 32–64 minutes) when compared with the adolescents grouped by earlier SSTs.
• Every 1-hour delay in SST was significantly associated with 21 minutes longer 24-hour sleep duration, 16 minutes later sleep onset, and 39 minutes later sleep offset.