Quinn Cooney of Mill Creek, Wash., is excited about starting high school in September, but she’s not looking forward to waking up at 5:30 a.m. to arrive on time. Classes for ninth-graders start at 7:30 a.m., 45 minutes earlier than they did in middle school.

“I think it is going to be harder to get up,” said Quinn, 13. “I do think it is better to start early so that we can be finished early and do things after school, but I am worried that if I have a boring class for my first period that it will be hard to stay awake.”

Decades of sleep research have confirmed what parents know: It’s hard for teenagers to wake up early. Some high schools have adopted later starts, around 8:30 a.m., to improve attendance and performance. But other districts say it’s too complicated to shift schedules because of logistics involving buses and after-school activities.

About 40 percent of U.S. public high schools open before 8 a.m., according to the U.S. Department of Education’s National Center for Education Statistics, with just 15 percent starting 8:30 a.m. or later. In districts where early starts are necessary because the same bus does multiple runs for high school, middle school and elementary students, teens often get the early shift.

That’s the case in Anne Arundel County, Md., where public high schools start at 7:17 a.m. and buses start running at 5:50 a.m. Lisa Rodvien taught high school there, in Annapolis, and says attendance at her first-period classes was “as low as 50 percent or below.” Among those who showed up, “I would definitely see three or four kids with their heads down. You walk over to them to wake them up and get them to sit up, and you see that they’re exhausted.”

Earlier this year, Anne Arundel school officials laid out options for delaying start times to anywhere from 7:32 a.m. to 9:45 a.m. along with potential complications, such as additional costs if buses are added, child care issues where late-day schedules might prevent teens from picking up younger siblings after school, and implications for teams if they end up playing in the dark. Bob Mosier, spokesman for Anne Arundel schools, said no decisions have been made.

Megan Kuhfeld, a graduate student at the University of California-Los Angeles who’s been studying late-start debates since she was an undergrad at Duke University in North Carolina, surveyed about 35 districts that switched to later starts and found most were glad they’d made the switch. Not only did students benefit, for the most part, but “the things people had feared — how transportation would be affected, how sports would be affected — became the new normal and people adjusted,” she said.

But Kuhfeld knows firsthand the pros and cons of late-start high schools, having attended one in Chapel Hill, N.C. “I enjoyed waking up later than everyone in the area next to me where there were early start times,” she said, but as a member of the tennis team, she had to miss sixth and seventh period classes to compete at other schools. In junior and senior year, that meant AP classes had to be made up. “It was hard to balance everything,” she said. “I’d get home at 8 p.m. and hadn’t had dinner yet.”

Still, advocates say several studies show the benefits of late start schools outweigh the drawbacks. In 1996, high school start times in Edina, Minn., changed from 7:20 a.m. to 8:30 a.m. The change improved attendance, decreased tardiness and left kids more alert, better prepared and even less depressed and less likely to visit school nurses, according to studies led by Kyla Wahlstrom, director of the Center for Applied Research and Educational Improvement at the University of Minnesota. By the end of the first year, 92 percent of Edina parents also said they preferred the later start, Wahlstrom said.

Following Edina’s lead, Minneapolis, with an urban, low-income population that was very different from Edina’s affluent suburban kids, also decided to delay public high school start times, from 7:15 a.m. to 8:40 a.m. A five-year study there showed the new schedule “statistically improved graduation rates because kids who had been sleeping through their first hour were not short on credits,” Wahlstrom said. “When kids were short on credits, they would say, ‘I’m going to drop out of school.’” Today Minneapolis high schools start between 7:56 a.m. and 8:30 a.m., but none has gone back to 7:15 a.m.