Scientists have known for a while that the body’s 24-hour biological clock changes during puberty; teenage sleep patterns naturally shift to waking later in the morning and sleeping later at night. Now, new research from the University of California, Berkeley, and Northeastern Illinois University has found that early school start times may be taking a toll on teens’ grades.

Researchers tracked the personal daily online activity profiles of nearly 15,000 college students as they logged into campus servers. They sorted the students into three categories — night owls, morning people, and daytime people — based on their activities on days they were not in class. They then compared class times to academic outcomes for students in each group.

Their findings, published in the journal Scientific Reports, show that students whose circadian rhythms were out of sync with their class schedules — for example, night owls taking early morning courses — received lower grades and had lower grade point averages due to “social jet lag,” a condition in which peak alertness times are at odds with work, school or other demands.

“We found that the majority of students were being jet lagged by their class times, which correlated very strongly with decreased academic performance,” said the study’s co-lead author Benjamin Smarr, a postdoctoral fellow at UC Berkeley who studies circadian rhythm disruptions.

While students of all categories suffered from class timing-induced jet lag, the study found that night owls were especially vulnerable, many appearing so chronically jet lagged that they were unable to perform optimally at any time of day.

This social jet lag adds up.

The recommended amount of sleep for teenagers is roughly 9.25 hours each night. But instead, according other research, between early school start times, school work, extracurricular activities, and digital device use, average amount of sleep teenagers actually get is closer to seven hours. Each night a teen gets fewer than the optimal amount of sleep, they build up something called a sleep debt which, by the end of the week, totals close to 10 hours.

And it comes with a cost. Sleep is the mechanism by which teens learn. Between social jet lag and an ever-growing sleep deficit, it’s little wonder that grades are slipping.

The results suggest that “rather than admonish late students to go to bed earlier, in conflict with their biological rhythms, we should work to individualize education so that learning and classes are structured to take advantage of knowing what time of day a given student will be most capable of learning,” Smarr said.

This may be possible in a university setting, where coursework is by nature much more individualized, but it’s doubtful whether multiple start times that suit various circadian rhythms could be implemented in high schools. What is possible, however, is adjusting school start times to the average teenage sleep patterns, so teens can get the sleep they need to learn.

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