Falling Asleep In Class? Blame Biology

01/16/2009 05:12 am ET | Updated Nov 17, 2011
  • Madison Park cnn.com

Parents flick the light switch, flap the sheets and prod their groggy teenagers to get to school on time. Then, when the teenagers get to school, they slump over their desks to snooze.
Starting high school an hour later increased the number of hours teenagers slept and decreased car accident rates.

Starting high school an hour later increased the number of hours teenagers slept and decreased car accident rates.

Sleepy teenagers may not be able to help it, researchers say. Blame it on the early school start time and their circadian rhythms: the mental and physical changes that occur in a day.

Teenagers need eight to 10 hours of sleep, compared with the six to eight hours recommended for adults. Teenagers also tend to go to bed and wake later than adults. These biological tendencies clash with early morning high school schedules, leaving them sleepy in class.

Research conducted at the University of Kentucky in Lexington found that when Fayette County high schools delayed their start time by an hour, the percentage of students getting at least eight hours of sleep per night jumped from 35.7 to 50 percent.

The study, published Monday in the Journal of Clinical Sleep Medicine, surveyed 10,000 students in the Kentucky county before and after their schools changed the start time from 7:30 to 8:30 a.m.

Students have the most difficulty staying awake and functioning during early morning classes.

"It's as if they are jet lagged, like they've just flown into Atlanta from San Diego," said Dr. Barbara Phillips, a co-author in the study. "For people who live in Atlanta, it might be 8 a.m. For a teenager, it feels like it's 5 o'clock in the morning. They're sleepy and don't do well."

Read more on cnn.com