A 2008 study found that, in one town, delaying the school day by an hour reduced car crash rates amoung teens by over 16 percent. Now, a new study adds further evidence that starting the school day letting teens sleep in means fewer car crashes.
Researchers looked at two towns that were pretty much identical—except for the time that teens were expected to arrive at high school. In one county, the school day started at 7:20 a.m., and the researchers found that, among every thousand licensed drivers ages 16 and 17, there were about 53 car crashes over the course of a school year. In the other county, where school started at 8:45 am, that number was reduced to 37.
The researchers also found that in the early-start county, there were more run-off-the road crashes among teens. They suspect that these might be directly due to sleep loss.
"There is a growing literature that shows that early start times are a problem, and school systems should take a look at the data and seriously consider whether they should delay them," the lead study author told the New York Times. There's evidence that pushing the start of the school day later improves grades, as well as physical and mental health.
The Wall Street Journal explains why it's beneficial for teens in particular to sleep later during the week:
Biological changes associated with puberty result in a shift in circadian rhythms, causing adolescents to get tired later at night, sleep experts say. The changes can start in middle school and can shift a child's bedtime by as much as two hours. Exacerbating that physiological reality is teenagers' tendency to study late at night and to use electronics close to bedtime, when blue-light exposure can further delay sleep.
But some schools in the US. .are successfully shifting to a later start, according to Scientific American: "In hundreds of districts that have made the change, students do not have a harder time fitting in after-school activities such as sports or in keeping part-time jobs."