Teens who start school earlier in the morning are at increased risk for traffic crashes, a new study finds.

But starting the school day a little later seems to improve teens' attention and reduce impulsiveness, another study finds.

In 2008, the weekday traffic crash rate for 16- to 18-year-olds in Virginia Beach, Va., was about 41 percent higher than for the same age group in nearby Chesapeake, Va. High school classes started at 7:20 to 7:25 a.m. in Virginia Beach and at 8:40 to 8:45 a.m. in Chesapeake.

For every 1,000 teen drivers, there were 65.8 car crashes in Virginia Beach and 46.6 crashes in Chesapeake, the investigators found.

Similar differences were seen in 2007, the researchers said.

When the researchers focused only on the school months of September 2007 through June 2008, they found the weekday crash rate for teen drivers was about 25 percent higher in Virginia Beach than in Chesapeake -- 80 versus 64 per 1,000 teen drivers.

The research, originally presented last year at a meeting of the American Academy of Sleep Societies, is published April 15 in the Journal of Clinical Sleep Medicine.

Israeli researchers, reporting in the same issue of the journal, say pushing back school start times by just one hour appears to improve teens' mental functioning.

Their study of eighth-graders found that the 14-year-old students were more attentive and made fewer mistakes when school started one hour later. The students got about 55 minutes more sleep and did better on tests requiring attention, the researchers found.

Source: Businessweek