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The closer high school students get to graduation, the less they sleep.
In 2025, 31% of ninth graders got at least 8 hours of sleep on an average school night. Among 11th and 12th graders, the share fell to 20%, according to new Youth Risk Behavior Survey data from the Centers for Disease Control and Prevention.
So the students facing the biggest exams are running on the least rest, right as finals season makes the all-nighter look tempting. What does studying on that little sleep actually do to memory?
CDC: About 24% of High Schoolers Sleep 8 or More Hours on School Nights
Across all grades, roughly 1 in 4 high school students reached the 8-hour mark in 2025. The figure held flat from 2023 and sits below the 27% recorded in 2015.
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The American Academy of Sleep Medicine recommends 8 to 10 hours a night for teens ages 13 to 18. The CDC points to late bedtimes and early school start times as the reason most students fall short.
JAMA: Share of High Schoolers Sleeping 5 Hours or Less Rose From 16% to 23%
A research letter published in JAMA in March tracked the same survey across 16 years. The share of high schoolers sleeping 7 hours or less climbed from 68.9% in 2007 to 76.8% in 2023.
The increase came from the far end of the scale. Students reporting 5 hours or less rose from 15.8% to 23.0%, while the share sleeping 6 to 7 hours held steady. The authors add that teens tend to overestimate how much they sleep, so the real numbers may run higher.
Researchers have tested what a 5-hour night does to learning by setting that exact limit for a group of teens.
Teens Given 5 Hours in Bed Forgot More Crammed Words, While Spaced Study Held Up
In a 2016 study in the journal Sleep, researchers assigned 56 students ages 15 to 19 at a boarding school to a week of either 5 or 9 hours in bed each night. During that week, the students used digital flashcards to learn 40 difficult vocabulary words of the kind found on graduate school entrance exams.
Some words were spread across four days, and others were crammed into single sessions. Total study time stayed the same either way.
The sleep-restricted students forgot more of the crammed words at every follow-up test. For the spaced words, recall came out about even between the two groups. The authors concluded that spacing gave students strong protection against short sleep.
The study tested a week of 5-hour nights, which is a different setup from a single night with no sleep at all.
Students Who Cram May Not Know About Spacing, a Psychology Review Found
A release on a 2013 review of study techniques from the Association for Psychological Science says students who favor last-minute cram sessions may not be familiar with spacing. In the sleep study, spacing cost no extra time. The benefit came from the schedule alone.
Take the hours a student might sink into the night before an exam and spread them across the days before it:
Start several days out, so each topic gets more than one pass.
Keep the night before for a light review and a full night of sleep.
A timer keeps each session short enough to repeat the next day. Quizlet’s Pomodoro timer lets students start and stop short, timed study sessions on a set clock.
Parents can help on the sleep side too. The CDC suggests putting devices away at least an hour before bed and keeping phones out of the bedroom overnight.
Sleep Loss Rose Even Among Teens Without Risk Behaviors, JAMA Researchers Found
The JAMA letter also checked whether the slide in sleep was concentrated among teens with known risk behaviors, from heavy media use to substance use. Insufficient sleep rose as much or more among students without those risks.
The authors read that as a sign that structural factors affecting most teens are driving the trend, and they call for population-level solutions. Later school start times, they write, have been linked to longer sleep and to students who are more involved in school.
The CDC makes a similar call, suggesting that schools work with families and staff on later start times and add sleep lessons to the curriculum.
