SEATTLE — High school students are getting more sleep in Seattle, say scientists studying later school start times.

Teenagers wore activity monitors to find out whether a later start to the school day would help them get more sleep. It did, adding 34 minutes of slumber a night. They also reported less daytime sleepiness, and grades improved.

The Seattle School District changed from a 7:50 a.m. start time to 8:45 a.m. in the fall of 2016 for high schools and most middle schools, joining dozens of other U.S. school districts adopting later starts to help sleep-deprived teens.

Teenagers’ nightly sleep has decreased and most adolescents don’t get the recommended nine hours. One culprit: Light from devices that many teens use to chat, post and scroll long after dark.

Franklin High School senior Hazel Ostrowski, who took part in the study, said sleeping later makes it easier to pay attention during class but she still struggles sometimes.

“I’ll wake up so tired I wish I could go back to sleep. At night, I’ll be on my phone and I just want to stay up,” she said.

Researchers worked with science teachers at two high schools to find out if students got more sleep after the change or simply stayed up later. Over two years, they recruited 178 sophomores to wear wristwatch-like monitors for two weeks to track activity and light exposure. Results were published Wednesday in the journal Science Advances.

The scientists compared sleep habits of sophomores in spring 2016, before the change, to sleep habits of sophomores from spring 2017, after later start times went into effect.

Some measures held steady. Naps and weekend sleep schedules didn’t change. On school nights, only a few students stayed up later, not enough to greatly budge the average.

What changed was wakeup time, with morning activity starting about 45 minutes later on school days. Combined with a slight shift to later bedtimes for a few, the average sleep duration increased by 34 minutes.

Put another way, morning wakeup time shifted from 6:24 a.m. to 7:08 a.m. Falling asleep shifted only a tad, from 11:27 p.m. to 11:38 p.m.


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