California’s mandate requiring later start times for middle and high schools is 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 paper from the National Bureau of Economic Research said Senate Bill 328, 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 health experts. The largest jump was among boys.

The study shows that “rest and sleep are incredibly important in the function of schools,” 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’s first-year results are consistent with previous research linking better sleep to improved student well-being and academic performance. The study used changes in teachers’ 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 the law took effect in the 2022-2023 school year and tracking academic gains from 2022 through 2025.

California later school start times boost grades, sleep, study says - Los Angeles Times