Breaking the Early Bell: Lessons from the First Statewide Mandate on School Start Times

California’s Senate Bill 328 is the first statewide mandate on school start times. Using difference-in-differences designs across four data sources, we find that the mandate increased the share of students sleeping at least 8 hours by 13%; mental health effects point toward improvement but are imprecise. High schools in counties with earlier pre-policy start times gained 1.7–1.8 percentage points in the share meeting state standards in math, English, and science, largest among Hispanic students. Suggestive evidence shows adolescents’ sports participation fell and shifted later; parents arrived at work later and were more likely to be at work after 4 p.m.