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California's later school start law lifted sleep, grades and mood, study finds

Students under California's mandate for later school start times are getting more rest, experiencing improved psychological well-being and achieving better results in math and English classes, according to a new National Bureau of Economic Research working paper reported by the Los Angeles Times. The law, Senate Bill 328, took effect in 2022 and sets 8 a.m. as the earliest opening bell for most middle schools and 8:30 a.m. for high schools, the paper says.

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Sleep gains tied to mental health and test scores#

The share of students getting at least eight hours of sleep nightly, the minimum health experts recommend for adolescents, climbed 13% under the new law, with boys showing the biggest jump, the Los Angeles Times reports. Study author Osea Giuntella, a University of Pittsburgh researcher, said the rise in sleep was moderate but still yielded gains in how students felt emotionally and performed in their classes, according to the Los Angeles Times.

Boys reported the steepest drops in sadness and hopelessness, while Latino students saw the biggest easing in trouble concentrating, the paper found, per the Los Angeles Times. Giuntella said the first-year results line up with earlier research connecting better sleep to student well-being and academic performance, the outlet reports.

To estimate the effect, researchers tracked shifts in teachers' commute arrival times recorded in the American Community Survey as a proxy for when classes actually began, then compared student outcomes across the 2022-23 school year and academic results running through 2025, the Los Angeles Times reports. Terra Ziporyn, executive director of the nonprofit Start Schools Later, described the measure as instrumental to California's efforts addressing what educational institutions have identified as a student mental health crisis, according to the outlet.

A body clock that shifts later during adolescence#

Puberty pushes the internal clock governing sleep and wakefulness later in the day, so teenagers tend to feel alert further into the night than adults do, which is why many struggle to fall asleep early enough for school, ScienceDaily reports. University of Zurich developmental pediatrician Oskar Jenni said chronic sleep loss harms overall wellness, emotional functioning, bodily growth and academic performance, according to ScienceDaily.

In a Swiss system that let students choose when to start their day, arriving as early as 7:30 a.m. or as late as 8:30 a.m. when regular classes began, 95% chose the later option, starting on average 38 minutes later than under the earlier schedule, ScienceDaily reports.

Earlier research abroad linked timing to anxiety#

A separate line of research has tied the mismatch between school schedules and the adolescent body clock to anxiety. The National Youth Policy Institute found that South Korean high school students average six hours of nightly sleep, short of the eight hours doctors recommend, based on a survey of 8,759 students, the Seoul Economic Daily reports. A University of Southampton paper in Sleep Medicine Reviews, drawing on a meta-analysis of 235,526 participants across 12 studies, found that larger gaps between weekday and weekend sleep timing, called social jet lag, were associated with more severe anxiety symptoms, though the effect size was small, according to the Seoul Economic Daily.

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