California’s Statewide Shift to Later School Start Times Shows Early Gains in Sleep, Health and Academics

In 2022 California enacted Senate Bill 328, a statewide mandate requiring most middle schools to begin no earlier than 8 a.m. and high schools no earlier than 8:30 a.m. The law took effect for the 2022-2023 school year and has been tracked through 2025 by a working paper from the National Bureau of Economic Research.

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The NBER analysis used teachers’ commute arrival times from the American Community Survey as a proxy for the timing shift. Compared with the pre-SB 328 period, the study reports:

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• A 13 % increase in the share of students obtaining at least eight hours of sleep per night.

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• The largest sleep gains were observed among boys.

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• Self-reported mental-health indicators improved, with boys showing the greatest reductions in sadness, hopelessness and suicidal ideation, and Hispanic students reporting the biggest drop in concentration difficulties.

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• Academic performance rose for eighth-grade students in both math and English, especially among Hispanic and economically disadvantaged learners.

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Sports and extracurricular activities did start later, but the timing shifts were statistically insignificant. Some students delayed bedtime slightly, yet overall morning sleep increased.

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• Terra Ziporyn, executive director of the nonprofit Start Schools Later, frames SB 328 as a central element of California’s response to a student-mental-health crisis, arguing that preventing systematic sleep loss is a primary preventive measure. She notes that the law’s implementation could be strengthened by statewide data collection to better assess impact.

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A segment of parents has voiced practical worries: later start times may complicate work commutes, push back sports and extracurricular schedules, and encourage some students to stay up later. Districts reported varying capacities to manage the transition.

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• Some districts described the shift as “too hard and too expensive,” citing limited guidance from the state Department of Education.

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• San Francisco Unified School District partnered with operations experts to redesign bus routes, producing roughly 1,000 feasible schedules, saving the district about $5 million, and leaving a majority of families and staff satisfied with the change.

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Early evidence suggests that a uniform, state-level policy can produce measurable health and academic benefits, particularly for groups historically facing sleep disparities.

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• “The first step in addressing student mental health problems is to not create them in the first place,” — Terra Ziporyn

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• “California set a huge precedent for the whole nation by saying, ‘We cannot leave what is essentially a public health decision in the hands of local districts,’” — Terra Ziporyn

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• “This happens often with some shock to individual and families’ habits, and so it also requires the ability to navigate this transition in a way that doesn’t backfire,” — Osea Giuntella, an author of the report

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The study’s authors recommend that California collect comprehensive, statewide data on school start times to refine impact assessments and guide future adjustments. No specific legislative deadlines or hearings are mentioned in the sources.

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