In a March study funded by the Centers for Disease Control and Prevention, researchers at the University of Minnesota found a 65%-to-70% decrease in vehicle crashes among 16- to 18-year-olds in two high schools, in Wyoming and Minnesota, excluding crashes caused by unrelated factors, such as intoxication.
The study looked at more than 9,000 high-school students in five districts in Wyoming, Minnesota and Colorado that had delayed school start times to the 8 a.m.-to-8:55 a.m. window. The researchers compared attendance records, academic performance, mental health and car-crash rates before and after the changes to start times.
"The later the start time, the more that we had positive outcomes in all measures," said Kyla Wahlstrom, director of the Center for Applied Research and Educational Improvement at the University of Minnesota and the study's lead researcher. "There were cumulative benefits based on the later start."
Dr. Wahlstrom said her research and other studies by the CDC have found eight hours of sleep appears to be the dividing line in terms of risky behaviors by teens. Getting less than eight hours increases the risk of taking drugs or alcohol, for example.
See the article in the Wall Street Journal for more information on the benefits of a later start time for high schools.