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California鈥檚 mandate requiring later start times for middle and high schools is already yielding results, with students sleeping more, reporting better mental health and scoring higher math and English scores, according to a new study.

The new working from the National Bureau of Economic Research examines the effects of Senate Bill 328, California鈥檚 statewide mandate for later school start times. The law, which went into effect in 2022, requires most middle schools to start no earlier than 8 a.m. and high schools no earlier than 8:30 a.m.

The study found that the new law increased the share of students sleeping at least eight hours per night by 13%, meeting the minimum recommended for adolescents by . The largest jump was among boys.

The study shows that 鈥渞est and sleep are incredibly important in the function of schools,鈥� said Osea Giuntella, an author of the report. Although the short-term increase in sleep is moderate, it has led to significant improvements in mental health and academic outcomes, he said.

Giuntella, a University of Pittsburgh researcher who studies sleep and economics, said the study鈥檚 first-year results are consistent with previous research linking better sleep to improved聽student well-being and academic performance. The study used changes in teachers鈥� commute arrival times from the American Community Survey as a proxy for later school start times, comparing sleep and mental health data before and after SB 328 took effect in the 2022-2023 school year and tracking academic gains from 2022 through 2025.

Gains in sleep, mental health, English and math

Students reported experiencing better mental health since schools shifted to later start times, with boys reporting the largest reductions in sadness, hopelessness and suicidal ideation, and Hispanic students reporting the biggest drop in difficulties concentrating.

Terra Ziporyn, executive director at nonprofit Start Schools Later and longtime advocate of later school start times, said SB 328 was a key part of California鈥檚 response to what schools have described as a student mental health crisis.

鈥淭he first step in addressing student mental health problems is to not create them in the first place,鈥� Ziporyn said. 鈥淵ou can get a lot of counselors, but systematically depriving an entire adolescent population of adequate sleep is a surefire way to hurt their mental health.鈥�

The study also found significant improvements in academic achievement, with eighth grade students making measurable gains in math and English, particularly among Hispanic and economically disadvantaged students.

Giuntella, the study鈥檚 author, said the improvement in scores was likely 鈥渓argely driven by the change in sleep鈥� based on comparable where increased sleep led to higher GPAs. That鈥檚 also why Hispanic students, who are already less likely to get adequate sleep than white students due to lower family income and family and work responsibilities, improved their math and English scores the most, Giuntella said.

Parents struggle with new schedules

The state mandate is the only one in the nation.

鈥淐alifornia set a huge precedent for the whole nation by saying, 鈥榃e cannot leave what is essentially a public health decision in the hands of local districts,鈥� 鈥� Ziproyn said. 鈥淚t鈥檚 not just a negotiable school budget item that you trade off against anything else.鈥�

But some parents have said later start times complicate work commutes, push back sports and extracurricular activities and lead to some students simply pushing back the time they go to bed.

The study found that sports and extracurricular activities did start later after the change to later start times, but the changes were 鈥渕arginal and not statistically significant,鈥� Giuntella said.

鈥淎nd it鈥檚 true that, yes, students may even go to bed a little later than they were, but they are definitely sleeping in more in the morning,鈥� she said.

Guintella described later start times as just 鈥渙ne institutional factor鈥� that may help address a complex sleep-deprivation problem, pointing to issues like the rise in nighttime screen use.

鈥楾oo hard and too expensive鈥� for some districts

Some school districts found the transition to later school start times 鈥渢oo hard and too expensive,鈥� Ziporyn said. Ziporyn said district administrators could have received more guidance from the state Department of Education to explain the benefits of later start times, and involve families in finding solutions to logistical problems.

鈥�(Schools) have to fully understand why this is being done and communicate it with confidence to the community that they鈥檙e doing the right thing for kids,鈥� Ziporyn said.

San Francisco Unified, for example, worked with operations experts at the Yale School of Management, Georgia Tech University and Northwestern University to redesign their bus routes in response to the change. With more than 120 schools and 18 different start times, the district generated about 1,000 new feasible bus schedules, which ended up saving the district about $5 million and with a majority of families and staff members satisfied with the transition to later start times, according to a report by

But most schools in California did not have access to dedicated consultants to ease the transition, Ziporyn said.

鈥淐alifornia could have improved making these resources more readily available to the districts,鈥� Ziporyn said. 鈥淏uilt into the law was that there was supposed to be help from the state Department of Education about getting this done, and building that community buy-in is part of it.鈥�

Giuntella said the state can improve its implementation of SB 328 by collecting statewide data on later school start times to 鈥渁ssess the impact of the reform.鈥� In the meantime, schools can take from the study that later start times are 鈥渆ffective and powerful tools鈥� for student outcomes.

鈥淭his happens often with some shock to individual and families鈥� habits, and so it also requires the ability to navigate this transition in a way that doesn鈥檛 backfire,鈥� Giuntella said.

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