SEATTLE (AP) -- Researchers at a sleep conference say they have another reason high school classes should start later in the day: Letting teens snooze a little longer might mean fewer car crashes.
When high schools in one county of Kentucky started school at 8:30 a.m. instead of 7:30 a.m., their students' accident rate dropped dramatically, a University of Kentucky scientist told the annual meeting of the Associated Professional Sleep Societies on Tuesday.
''It's the sort of thing that other districts ought to look at. ... Students are getting dramatically less sleep than they need at that age to function well,'' Dr. Fred Danner, an expert in cognitive and intellectual development, told The Seattle Times.
Danner's study began after the school board in Fayette County, Ky., pushed back the morning bell in 1998, in response to pressure from parents and others. He compared collision statistics involving teens for the two years before and the two years after the schedule change.
The crash rates for 17- and 18-year-olds in Fayette County dropped nearly 16 percent over the period while the rate for the same age group in the rest of the state increased about 9 percent.
Danner said the results do not prove a cause-and-effect relationship.
But, he said, ''These data are consistent with the idea that allowing adolescents to sleep more has a measurable effect on their own safety.''
For years, sleep researchers have campaigned for later high-school start times, saying teens' biological clocks don't allow them to be attentive early. Teens generally need about nine hours of sleep but get seven or less.
''Their brain is still really on the pillow, but we want their body in the classroom,'' said Dr. Mary Carskadon of Brown University Medical School, an expert on adolescent sleep and one of the conference speakers.
Danner said his study did not find any improvement in students' grades with the later start time. But a Minneapolis study reported slightly better grades when the start time switched from 7:15 a.m. to 8:40 a.m. in 1997. The study also said students were much less likely to miss classes, behaved better and experienced less depression.
Seattle School District officials have discussed changing the local 7:45 a.m. start time but, like other school systems across the nation, have been hindered by collateral issues.
Any change would require alterations in the transportation system and the scheduling of extracurricular activities, especially those that mesh with other school districts. There's also the problem of teens with after-school jobs.
Most area school districts have kept their start times between 7 and 7:50 a.m.
But this fall, after a yearlong study, Mercer Island High School east of Seattle will move its start time from 7:20 a.m. to 8 a.m. The need for more buses to meet the schedule was filled by providing state-financed Metro passes to students who need them.
''The research seems to be pretty consistent that they need about nine hours of sleep ... and the earlier the start, the more you're taking away from that,'' said Bill Keim, Mercer Island district superintendent.
The sleep conference, held at the Washington State Convention and Trade Center, ends Thursday. More than 4,000 researchers, physicians and other professionals are attending.
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