By Robert Preidt
Researchers followed 94 children and teens for two years, to learn how their sleep habits changed as they grew older.
A typical 9-year-old went to sleep at 9:30 p.m. and woke up at 6:40 a.m. during the school week. By age 11, the same child would go to sleep at 10 p.m. and wake up at the same time, the investigators found.
A typical 15-year-old went to sleep at 10:35 p.m. and woke up at 6:20 a.m. on a weekday. By age 17, the same teen went to sleep at 11:05 p.m. and woke up 6:35 a.m.
On weekends, the participants stayed up later but got more sleep because they were able to sleep later, according to the study published Nov. 7 in the journal PLoS One.
"There are changes in sleep, even as early as middle school," study author Stephanie Crowley, an assistant professor at Rush University Medical Center in Chicago, said in a Brown University news release.
Crowley was a graduate student at Brown University when the study was conducted.
Recently, the American Academy of Pediatrics recommended that classes at middle and high schools should not begin before 8:30 a.m.