As high school officials across the country are debating if later start times are better for the health and performance of students, a new School of Public Health study shows that later starts are indeed associated with improved mental and behavioral health for adolescents.

The study is published in the journal Sleep Health.

In 2014, the American Academy of Pediatrics recommended that all high schools start no earlier than 8:30 a.m. This suggestion came off the heels of mounting scientific evidence that early high school start times negatively had an impact on adolescent sleep duration, performance in school, and safety. Still, fewer than 15 percent of U.S. high schools comply with the recommendation.

“Although many school administrators know that early start times can harm students academically, the health consequences of chronic sleep deprivation are not as well known to them,” says study co-author, former high school teacher, and PhD student Aaron Berger. “We wanted to be able to provide schools with data to inform their decisions on school day scheduling.”

Berger and Associate Professor Rachel Widome partnered with other researchers to survey more 9,000 students from eight high schools in five districts across the U.S. on sleep and certain health, academic, and behavioral issues. The schools in the study had start times ranging from 7:35 a.m. to 8:55 a.m.

The study found that adolescents attending schools with later start times reported greater sleep duration and later wake-up times, which were also associated with better mental health outcomes.

For each additional hour of sleep reported, there was a 28 percent reduction in students who said they felt unhappy, sad, or depressed. Longer sleep durations were also associated with fewer students reporting use of alcohol, cigarettes, and other substances.

The researchers said that if schools can improve adolescents’ sleep by delaying their start times, and, as a result, enable adolescents to go through high school with better overall mental health and with less substance use, this is not only beneficial to their school experience, it will also set them up for success in their adult lives.