Places that have already pushed back school start times have repeatedly seen positive results. When Seattle’s public-school district shifted its start time in 2016 (from 7:50 a.m. to 8:45 a.m.), students got a median of an additional 34 minutes of sleep a night as a result. And in Cherry Creek, a Denver-area suburb, high schoolers slept about 45 minutes longer on average, and those improvements endured even two years after the change.

Despite success stories like these around the U.S., the national sleep statistics for teens remain dismal. In 2007, when the CDC first started asking about teen sleep in the national Youth Risk Behavior Survey, only 31 percent of high schoolers said they got at least eight hours of sleep on school nights. By 2019, that had slid to 22 percent.

That’s quite concerning, given that eight hours is actually the minimum amount they need.

Teen-sleep deprivation affects grades, attendance, and graduation rates. It leads to greater risk of injury for adolescent athletes, and more drowsy-driving crashes. And it worsens mental-health issues—including anxiety and suicidality. That’s profoundly unsettling, particularly in light of data released by the CDC in April showing that 44 percent of high schoolers said they’d had “persistent feelings of sadness or hopelessness” during the past year, and 20 percent had seriously contemplated suicide.