California teenagers can snooze a little later this year, thanks to a newly implemented law that says most high schools and middle schools cannot start before 8:30 a.m. and 8 a.m., respectively.
That law—the first in the country to set statewide mandates for school start times—isn’t only big for California students, but also for public-health experts fighting against what the American Academy of Pediatrics (AAP) has called an “epidemic” of teen sleep deprivation. Both the AAP and U.S. Centers for Disease Control and Prevention have long opposed early-morning class times and advocated for middle and high school bell times no earlier than 8:30 a.m.
Delayed school start times are an attempt to help teens get more sleep, which research shows is a big problem in the U.S. Only about 30% of high school students get their recommended eight hours of sleep on school nights, according to CDC data. Studies suggest sleep deprivation can put teenagers and adolescents at increased risk for obesity, substance use, depression, and poor academic performance, among other issues.
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Research has long shown that circadian rhythms—light-mediated internal cues that help regulate sleep—change throughout the lifecycle. That’s, in part, why adults may find themselves naturally rising earlier as they age. Teenagers’ body clocks, meanwhile, are best synced to bedtimes around 11 p.m. or midnight and wake times about nine hours later—a timeline that’s impossible when classes start before 8 a.m.
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Early school schedules are largely a holdover from when most families didn’t have two working parents and thus didn’t need to worry about adhering to a 9-to-5 schedule. The juggling act of scheduling bus routes, classes, athletics, and other extracurriculars has kept bells ringing early.
But these schedules are not grounded in science. The mismatch between teenagers’ internal rhythms and external schedules sets them up to fail, studies have long suggested. One 1998 paper found that when a small group of students started school about an hour earlier than they had previously, they experienced “significant sleep deprivation and daytime sleepiness.”
Moving start times back has been shown to have the opposite effect. A 2002 study conducted five years after seven public high schools in Minneapolis switched their start times from 7:15 a.m. to 8:40 a.m. found that the shift allowed kids to get about an hour of extra sleep per night; students also reported better attendance and fewer symptoms of depression. In a 2010 study, researchers examined students at a Rhode Island high school after it moved its start time from 8 to 8:30 a.m and found that students got an additional 45 minutes of sleep per night, while reporting less fatigue and better moods.
More recently, a study published in 2021 found that significantly more Denver-area middle and high school students got sufficient daily sleep after the local school district delayed start times by 40 to 70 minutes. Another 2021 study on Colorado students found that those who started school before 8:30 a.m. were slightly more likely to attempt suicide than peers who started later, though the results were not statistically significant. While more research is needed, and plenty of confounding variables may muddy the link, the findings suggest that starting classes later could improve teen mental health.
But changing bell times isn’t a panacea. A February 2022 research review that examined links between later start times and academic achievement found mixed results, with some schools reporting positive effects and others reporting negative or unclear consequences of the change.
There are also many logistics to contend with. In 2016, public schools in Durham, N.C., moved their start times from 7:30 a.m. to 9 a.m. In a survey conducted the following year, only 26% of school personnel said kids were better rested, and just 14% said they were learning more. Only 13% of school staff and 27% of parents wanted to keep the new schedule. Why? The drastic shift meant the school day ended later, pushing extracurriculars, after-school jobs, and homework later into the evening, and sometimes keeping kids up well past their former bedtimes.
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In 2018, schools in Newport, R.I., reverted back to their original start times after a two-year experiment with later bells produced a number of logistical headaches, including difficulty coordinating with nearby schools and scheduling extracurriculars. Transportation can also be an issue, whether it’s rejiggering bus schedules, contending with traffic patterns, or finding ways for working parents to drop off kids later in the morning, some schools have learned after pushing their schedules later.
California teacher Jeremy Adams raised many of these concerns in a January Cal Matters op-ed, adding that the new state law will inconvenience teachers who have to stay on campus for extracurriculars that begin after the academic day ends. “Ultimately,” Adams wrote, “this law will become a case study in ‘unintended consequences.’”
The school start time debate is still an area of active research. A team in Colorado, for example, is studying how changing school start times affects not just students’ health, but also that of their families, teachers, and wider community. And all eyes will be on the statewide shift in California, as education researcher Deborah Temkin told NBC News after the policy first passed in 2019. “If this turns out to be successful, with relatively few consequences, then I think it’s something that other states will likely consider,” Temkin said.
With the academic year only just beginning, it’s too soon to say how the experiment will turn out. But as some California high schoolers told the Mercury News, it’ll take more than a later starting bell to cure their fatigue. “When you’re in high school, no matter what time you wake up, you’re going to be tired,” said senior Anika Bose. “At least I have time to grab a coffee before class now.”
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Write to Jamie Ducharme at jamie.ducharme@time.com