Okay, let’s be perfectly clear about this. The study put out by Robert Vorona of Eastern Virginia Medical School and his colleagues did not prove that letting teenagers start school later would prevent them from getting into car accidents. However, those two effects were strongly correlated with each other.
It’s no surprise that teens are tired in the morning. Their circadian rhythms are shifted compared to younger children or adults such that teenagers tend to stay up later and want to sleep in later. Experiments on starting high schools later in the day have shown that such practices increase student attention span and academic success.
For this study, the researchers compared teen car crash rates in two neighboring Virginia cities, Virginia Beach, where high schools classes begin at 7:20 am, and Chesapeake, where the high schools begin at 8:40 am. In 2008, the teen crash rate was 41% higher in Virginia Beach. Traffic conditions did not suggest any other reasons for the difference in accident rates. In fact, the teen crash rates in both regions were highest at the time the kids would be going to school in the morning, and again for a few hours after school let out.
Again, these results are correlations and do not prove any causation between school start times and car crashes. The authors are planning more studies to further understand the ramifications of school start times. In the meantime, if your community is debating when to set school start times, you may want to bring this study to the attention of the school board.