By Stephanie Stahl

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PHILADELPHIA (CBS) — Teenagers may not be getting enough sleep. New research is adding fuel to the argument that school start times should be moved back.

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Most high school students don’t get the recommended eight to 10 hours of sleep a night. Experts say a big part of the problem is that most school classes start around 7:30 a.m.

The new study shows that students do better when classes start later.

Mornings are a little easier for Hazel Ostrowski, a high school senior in Seattle. She’s able to sleep in a bit longer thanks to a later start time of 8:45 — set in place by her school district two years ago.

“I think I definitely felt more awake especially in class when I had an extra hour of sleep,” Ostrowski said.

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Ostrowski was one of more than 170 students who took part in a new study that found when school started later, students slept longer and their academic performance improved.

“I think that really helped me complete my school work, but also just be more interested in what I was learning,” she said.

Researchers used wrist monitors to measure how long two different groups of sophomores slept.

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One group was monitored in 2016 when school started at 7:50, and the other group in 2017 when classes began almost and hour later at 8:45 a.m.

“I have seen that there are far fewer tardies and absences in the first period,” biology teacher A.J. Katzaroff said.

Katzaroff worked with researchers on the study and saw improved student performance first-hand.

“I see kids are generally more engaged in the work at the classroom,” Katzaroff said. “So very much more willing to participate than in the past.”

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While the study has shown positive results for students’ health and academics, it did not address potentially negative impacts on their after-school activities, which now might take place after dark.

“When you push the time back, it can be kind of difficult,” Ostrowski said.

Four years ago, the American Academy of Pediatrics recommended that middle and high schools start no earlier than 8:30 a.m., declaring chronic sleep loss among teens one of the most “easily fixable” public health issues facing Americans.

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One year later, the Centers for Disease Control and Prevention issued the same recommendation, but the later out time makes that difficult, which is why it hasn’t happened it many districts.

Stephanie Stahl