The American Pediatric Association recently released a statement that middle and high school students start school at 8:30 AM or later. Sleep-related research supports the later school start time so that adolescents can get more sleep per night. The recommended amount of sleep for teenagers is 8.5 to 9 hours per night, with the majority of teens not getting close to that. Chronic sleep deprivation has been linked with obesity, diabetes, mental health problems, and reduced academic performance.
The statement goes on to explain that teens lack of sleep is complex and involves homework, extracurricular activities, after-school jobs and use of technology that can keep them up late on week nights. So just delaying school start times may not improve teens' sleep duration if other lifestyle changes are not made. The most obvious one is restricting screen time at night.