California's later‑start school law improves sleep, mental health and test scores, study shows

A recent NBER study finds that California's Senate Bill 328, which pushed back middle‑ and high‑school start times, has increased average sleep, lowered depressive symptoms, and boosted math and English test scores, particularly among Hispanic and low‑income students. California's statewide mandate to push back the start of middle and high schools has already started to show measurable gains for students, according to a comprehensive new study released by the National Bureau of Economic Research. The research, focused on Senate Bill 328 or SB 328, evaluates the impacts that took hold in the 2022‑2023 academic year. Under the law, most California middle schools begin no earlier than 8 a.m. and most high schools start no earlier than 8:30 a.m. The authors of the report, led by University of Pittsburgh faculty member Osea Giuntella, found that the new start times lifted the proportion of students who slept eight hours or more each night by as much as 13 percentage points - a figure that aligns with the American Academy of Pediatrics' recommendation for adolescents. Beyond the obvious increase in sleep duration, the study examined a wider array of outcomes. Survey data collected before and after the policy's implementation revealed significant shifts in mental health markers. Students across the state reported lower rates of sadness, hopelessness and suicidal ideation, with boys showing the largest decreases in these symptoms. In addition, Hispanic students experienced the biggest reduction in reported difficulties with concentration. These outcomes dovetail with Giuntella's earlier work linking adequate sleep to emotional resilience. The researchers also tracked academic performance, using standardized test scores from the Common Core State Standards and California's own assessment system. Eighth‑grade students, the first cohort exposed to the new schedules, showed measurable gains in both math and English proficiency, and the effects were most pronounced among Hispanic and economically disadvantaged populations. The analysis suggests that these improvements are largely attributable to the increase in sleep hours, because prior studies have documented a positive relationship between sleep quality and GPA. The report acknowledges that shifting school start times is not a panacea and raises practical concerns that districts must still negotiate. A number of parents and some school trustees expressed difficulties relating to commute schedules, as well as potential interference with after‑school sports and other extracurricular activities. Giuntella reassured readers that while the new schedules did result in a slight shift of certain extracurricular events to later in the day, the changes were largely marginal and statistically insignificant. Conversely, the study underscores that the most significant effect was an increase in morning sleep, even if some students opted to go to bed slightly later. According to the authors, a policy that effectively removes insufficient sleep as a systemic risk factor offers a meaningful, low-cost intervention that can be bundled with other resources such as mental health counseling. Critics of SB 328 point out the additional logistical and financial burdens associated with the transition. Some school districts reported that the shift was "too hard and too expensive," citing the need for new transportation itineraries and staff scheduling adjustments. San Francisco Unified's experience illustrates how districts have sought external expertise-from the Yale School of Management to the Georgia Tech Faculty-to redesign bus routes and coordinate with parents. Ziporyn, the executive director at Start Schools Later, stressed that for many districts it will be vital to receive comprehensive guidance from the state education department as well as to forge partnerships with families so that the benefits of later starts can be disseminated without overwhelming administrative overhead. At a policy level, SB 328 represents, according to several analysts, a bold step in recognizing adolescent health as a critical public defile. By enacting a state‑wide mandate, California avoided the piecemeal approach that historically leaves variation in curriculum schedules to local districts. As Giuntella notes, the policy sends a clear message: sufficient sleep is not a negotiable line item on the school budget it is a public health imperative. The continuing evaluation of the bill, with data planned through 2025, will shed further light on whether the early gains in sleep, mental health, and academic performance sustain over time and translate into longer‑term educational outcomes such as higher graduation rates and reduced dropout incidence