New research shows that pushing back the school bell helps teens sleep more, think faster, and feel less drained during the day
If your teenager drags out of bed every morning looking like they haven’t slept in a week, there’s a good reason for that. They probably haven’t, at least not enough.
A new study published in Scientific Reports found that delaying the school day by just one hour gave early adolescents about 26 more minutes of sleep each night, less daytime tiredness, and measurably sharper thinking.
These aren’t just feel-good numbers. They come from a carefully designed, randomized study in France, where researchers tracked 7th and 8th graders over an entire school year.
Why Teenagers Struggle with Early Mornings
Your teen isn’t being lazy when they can’t get up. Their body is working against them.
During puberty, the brain’s internal clock shifts naturally toward later bedtimes and later wake times. The brain releases melatonin, the chemical signal for sleep, later in the evening than it does in children or adults. Teenagers aren’t choosing to stay up late. Their biology pushes them there.
When school starts at 7:30 or 8:00 a.m., that natural shift collides head-on with an early alarm. The result is chronic sleep loss, the kind that builds up week after week and doesn’t go away until summer.
Researchers have called this collision “the perfect storm.”
What the Study Found
Researchers at a French boarding school divided four classes of 12- to 14-year-olds into two groups. One group kept its 8:00 a.m. start. The other shifted to 9:00 a.m. starting in November. Researchers then measured sleep using wrist devices called actigraphs, tested thinking skills, and tracked how tired students felt during the day.
Six months later, the results were clear.
Students who kept the 8:00 a.m. start lost about 16 minutes of sleep per night over the course of the study. That’s a natural pattern during adolescence: as the school year drags on, sleep erodes.
Students in the 9:00 a.m. group picked up about 7 minutes of sleep per night. That may sound small, but the gap between the two groups added up to 26 minutes of sleep each night by the end of the study.
By February, half of the early-start students slept less than 7 hours a night. In the later-start group, only 1 in 8 fell below that threshold.
The Thinking Difference
Sleep isn’t just about feeling rested. It shapes how the brain works, and this study measured that directly.
Students in the later-start group performed significantly better on a test of inhibitory control, the ability to stop an automatic response and think before acting. That skill sits at the heart of impulse control, decision-making, and self-regulation.
The earlier-start students saw no improvement on this test. Their scores slipped slightly.
A second test of sustained attention showed a similar trend, with the later-start students making fewer impulsive errors.
This matters because adolescents who are chronically sleep-deprived are more prone to poor decisions, risky behavior, and emotional swings. These aren’t character flaws. They’re the predictable consequences of an underslept brain.
Did Students Just Stay Up Later?
One common concern about later school start times is that teenagers will simply shift their bedtimes later, cancel out any benefit, and sleep the same amount as before.
That’s not what happened here.
Bedtimes didn’t change significantly between the two groups. The later-start students woke up about 23 minutes later, but they didn’t go to bed much later. They just slept longer.
This pattern has shown up consistently across multiple studies. The body clock shifts during adolescence, but it doesn’t shift as far as the alarm clock would demand. A later start gives teenagers time to close that gap.
Who Benefits Most?
Not all teenagers responded equally. Students who described themselves as natural “evening types,” meaning those who naturally prefer staying up and sleeping in, gained the most from the later start. They added nearly 29 extra minutes of sleep compared to evening-type students in the early-start group.
Students who are naturally more morning-oriented saw less benefit, though they didn’t lose ground either.
As puberty progresses, more teenagers shift toward evening preferences. That means the benefits of a later start are likely to grow as kids move through high school.
A Real-World Caveat
Even with a 9:00 a.m. start, the students in this study averaged about 7 hours and 30 minutes of sleep per night. That’s better, but still below the 8 to 10 hours that most health organizations recommend for teenagers.
A later school bell helps, but it doesn’t solve everything. Evening screen time, homework deadlines, extracurricular activities, and social pressures all chip away at sleep. A later start gives teenagers a fighting chance. Building good habits around the rest of it is still part of the picture.
A Light Solution
It will take an act of congress to change school times. Short of that, a dawn simulator in morning and blue-light blocking glasses at night can help night owls adjust to these routines.
The Bigger Picture
The National Sleep Foundation, the American Academy of Sleep Medicine, and the American Academy of Pediatrics all recommend that middle and high schools start no earlier than 8:30 a.m. Only about 18% of high schools in the United States meet that standard.
The barriers to change are mostly logistical: bus schedules, after-school sports, parent work hours. Those are real challenges, but this study adds to a growing pile of evidence that the cost of early school starts is real too, and that it lands squarely on the teenagers who can least afford it.
One hour. More sleep. Sharper thinking. Less exhaustion.
For many families, that case is already made.
—Chris Aiken, MD
Director, Psych Partners
Editor in Chief, Carlat Psychiatry Report
