School performance improves when adolescents sleep longer

Adolescents often do not receive the 8 to 10 hours of sleep recommended by the American Academy of Paediatrics due to both late sleep-start and early arousal to attend school. In 2016, the Seattle public schools decided to delay the start time of secondary schools from 7:50 to 8:45 a.m. To examine the effect of that policy change on sleep patterns, sleepiness, grades, and school attendance, investigators compared these measures at the same time of the year both pre– and post–policy change. Participants were sophomore students attending science classes in two public high schools. Sleep duration and light exposure were measured with sleep-wake activity wrist monitors. Results were as follows:

• Following the later start time, median sleep duration increased from 6 hours and 50 minutes to 7 hours and 24 minutes (+34 minutes) during school days (P<0.001) but was not different on non-school days.
• The effect of oversleeping on non-school days secondarily affecting sleep on school days (i.e., social jet lag) was examined and found to be lessened after implementing the later school start time.
• Exposure to light pre- and post-sleep was similar on non-school days but was later in the mornings on school days following the policy change.
• Later school start time was associated with less sleepiness and improved grades.
• Later school time was associated with fewer school absences and tardiness episodes in the high school with the greater proportions of disadvantaged and ethnic minority students but not in the other school.