Most evidence says yes. In a study published 12 October 2026 in JAMA Network Open, youths aged 12 to 21 in California, where state law sets later school start times, woke about 40 minutes later and slept about 38 minutes longer than peers in other states. Bedtimes barely differed: the extra sleep came from later mornings.
Key takeaways
- In a 2026 JAMA Network Open study of 724 US youths aged 12 to 21, the 106 in California woke about 40 minutes later and slept about 38 minutes longer than peers in other states.
- Bedtimes differed by only about 3 minutes: the extra sleep came from later wake times.
- Since 1 July 2022, California law has required public high schools to start no earlier than 8:30 AM and middle schools no earlier than 8:00 AM.
- When Seattle moved secondary schools from a 7:50 AM to an 8:45 AM start, sophomores’ median sleep, measured with wrist monitors, rose 34 minutes (Science Advances, 2018).
- The one change: when your morning start moves later, keep your bedtime and spend the extra time asleep.
What did the 2026 study find?
California youths slept about 38 minutes longer than peers elsewhere, and nearly all of it came from waking later. Lu Dong and Wendy Troxel analyzed RAND’s 2024 American Youth Panel, a nationally representative panel of US youths aged 12 to 21. Participants reported their usual school-day (or weekday) bedtime and wake time; sleep duration was the gap between them. Results were adjusted for age, sex and school enrollment.
| Measure | California vs other states (adjusted) |
|---|---|
| Wake time | about 40 minutes later |
| Sleep duration | about 38 minutes longer |
| Bedtime | about 3 minutes later (no real difference) |
| Falling asleep in class or at work | no clear difference |
Among middle and high school students only, the group the law targets, Californians slept about 24 minutes longer and woke about 29 minutes later. Other Pacific states showed no similar gap. Across the whole sample, the average bedtime was about 10:30 PM, and 30% said they had fallen asleep in class or at work. California was the first state to mandate school start times statewide, and the authors write that the findings are consistent with later starts as a population-level lever for adolescent sleep.
Why do teens fall asleep so late?
Biology pushes teen sleep later. Around puberty, most adolescents’ sleep and wake times shift up to 2 hours later than in middle childhood, partly because the nightly release of melatonin, the hormone that signals night, comes later, according to the American Academy of Pediatrics (AAP).
That makes an early bedtime hard to keep, however disciplined the teen, and it is why a 2014 AAP policy statement urged middle and high schools to aim for start times no earlier than 8:30 AM. A later start lets a teen wake later without fighting a body clock that is not ready for sleep. To see where your own rhythm leans, take the Body Clock Type quiz.
How much sleep do teens need?
Teens aged 13 to 18 need 8 to 10 hours of sleep per 24 hours, according to a consensus statement from the American Academy of Sleep Medicine (AASM). The AAP puts the optimal range at 8.5 to 9.5 hours.
Many fall short. A 2015 CDC report noted that fewer than one in three US high school students slept at least 8 hours on school nights, and found that only 17.7% of public middle and high schools started at 8:30 AM or later in the 2011–12 school year.
The arithmetic explains why. A teen who needs 9 hours and must wake at 6:15 AM for a 7:30 AM start has to be asleep by 9:15 PM, more than an hour before the average bedtime in the 2026 data. The AASM also notes that insufficient sleep in teenagers is associated with a higher risk of self-harm, suicidal thoughts and suicide attempts.
What does other research on later school start times show?
Other studies point the same way. Seattle moved its secondary schools from a 7:50 AM to an 8:45 AM start for the 2016–17 school year. Researchers had sophomores at two high schools wear wrist activity monitors for two weeks, one group before the change and another after it.
- Median school-day sleep rose 34 minutes, from 6 hours 50 minutes to 7 hours 24 minutes.
- Median wake time moved 44 minutes later; the shift in sleep onset was not statistically significant.
- Median science-class grades rose from 77.5% to 82%, and daytime sleepiness fell.
The AAP statement also cites a 3-year study of more than 9,000 students at 8 high schools: 33% slept 8 hours or more at a 7:30 AM start, versus 66% at 8:55 AM.
What is the one change to make?
When your morning start moves later, keep your bedtime where it is and let only the alarm move. That is the pattern in the California and Seattle data. The Seattle authors suggested that bedtimes could drift later over time, which would erode the gain.
- Start from your first fixed commitment: a class, practice, shift or meeting.
- Count back travel and getting-ready time to set your wake time.
- Count back the sleep you need (8 to 10 hours for teens aged 13 to 18) to set your bedtime.
- When a later start opens up, such as a later first class next term, move the wake time and keep the bedtime.
- Plan the night on My BodyClock as one Sleep block, so the gain shows up as sleep, not more evening.
College students can use the same rule; time blocking for student productivity and health shows how to lay out the rest of the day, and our guide to a caffeine cutoff time covers one afternoon habit that can push bedtime later. For students planning around their body clock, see Circadian Coaching and Student Flourishing.
What are the limits of this evidence?
The 2026 study shows an association, not proof that California’s law caused the difference. It was cross-sectional and self-reported, had no data from before the law, and included only 106 Californians, 48 of them in middle or high school. Daytime sleepiness did not differ. The Seattle study had no control group. Still, both point the same way: later mornings, same bedtimes, more sleep.
Your day on My BodyClock
The day above on My BodyClock shows a high school day with an 8:30 AM start. Sleep runs from 10:30 PM, close to the average bedtime in the 2026 data, to 7:15 AM: 8 hours 45 minutes. Getting ready, breakfast at home and the walk to school fit before the first bell. Classes, lunch, practice, homework and a family dinner fill the day, Flow blocks cover the transitions, and a wind-down with a book leads back to the same bedtime.
Swap in your own first commitment and count back. Build your version in Owaves: My BodyClock on the App Store, or join the Android waitlist.
FAQ
What time do California high schools start?
Since 1 July 2022, California law has required public high schools to start no earlier than 8:30 AM and middle schools no earlier than 8:00 AM. Rural school districts are exempt.
How much sleep does a teenager need?
The American Academy of Sleep Medicine recommends 8 to 10 hours per 24 hours for teens aged 13 to 18. The American Academy of Pediatrics puts the optimal range at 8.5 to 9.5 hours.
Do teens just stay up later if school starts later?
Not in these two studies. Bedtimes differed by only about 3 minutes in the 2026 California study, and the Seattle shift in sleep onset was not statistically significant; wake times moved later in both.
Sources
- Dong L, Troxel W. Sleep Duration and Daytime Sleepiness Among Adolescents. JAMA Network Open, 12 October 2026. doi:10.1001/jamanetworkopen.2026.38588. https://pmc.ncbi.nlm.nih.gov/articles/PMC13659564/
- Dunster GP, et al. Sleepmore in Seattle: Later school start times are associated with more sleep and better performance in high school students. Science Advances, 12 December 2018. https://pmc.ncbi.nlm.nih.gov/articles/PMC6291308/
- American Academy of Pediatrics, Adolescent Sleep Working Group, Committee on Adolescence, Council on School Health. School Start Times for Adolescents. Pediatrics, September 2014. https://pmc.ncbi.nlm.nih.gov/articles/PMC8194457/
- Paruthi S, et al. Recommended Amount of Sleep for Pediatric Populations: A Consensus Statement of the American Academy of Sleep Medicine. Journal of Clinical Sleep Medicine, 15 June 2016. https://pmc.ncbi.nlm.nih.gov/articles/PMC4877308/
- Wheaton AG, Ferro GA, Croft JB (CDC). School Start Times for Middle School and High School Students — United States, 2011–12 School Year. MMWR, 7 August 2015. https://pubmed.ncbi.nlm.nih.gov/26247433/
- California Department of Education. Waiver Frequently Asked Questions (SB 328, school start times). https://www.cde.ca.gov/re/lr/wr/faq.asp
If you’re in crisis in the US, call or text 988 (Suicide & Crisis Lifeline). Outside the US, contact local emergency services.
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