When teens want to sleep in on a school day, they’re not being lazy. For one, teens need more rest than adults: about eight or nine hours a night, compared with about the six or seven their parents require. Teens, biologically, really do crave sleep.

Which is a problem when it comes to education. Most high schools start before 8 am to help parents get to work by 9 am. Early school start times also give kids more time for after-school activities like sports or theater.

But that has consequences: Around 69 percent of high school students get less than eight hours of sleep on a school night, according to the Centers for Disease Control and Prevention, which puts these teens at risk of negative impacts on health.

There may be a simple fix: Start schools at a later time.

But it’s not a foregone conclusion that later start times will ensure teens sleep more. Later start times could lead teens to go to bed even later. Or parents might still wake them up early. When it made its recommendation, the Academy of Pediatrics admitted “it is clear that additional research is needed to further document the effects of changes in school start times over time.”

Well, there’s some new (but still incomplete) evidence that later start times do help teens get more sleep.