Science says teens need more sleep. So why is it so hard to start school later?

Reviewed by Megan Craig, M.Sc.Nov 6 2023

High school classes start so early around this city that some kids get on buses at 5:30 in the morning.

Just 10% of public schools nationwide start before 7:30 a.m., according to federal statistics. But in Nashville, classes start at 7:05 — a fact the new mayor, Freddie O'Connell, has been criticizing for years.

"It's not a badge of honor," he said when he was still a city council member.

Since his election in September, O'Connell has announced that pushing back school start times is a cornerstone of the education policy he is promoting. He and others around the country have been trying to stress that teenagers aren't lazy or to blame for getting too little sleep. It's science.

"All teenagers have this shift in their brain that causes them to not feel sleepy until about 10:45 or 11 at night," said Kyla Wahlstrom, a senior research fellow at the University of Minnesota in the College of Education and Human Development. She studies how education policy affects learning, and she used to be a teacher. "It's a shift that is biologically determined."

Sleep deprivation in teenagers is linked to mental health struggles, worse grades, traffic accidents, and more. That's why states including California and Florida have mandated later start times. Individual districts across the country — including some in Tennessee — have made the same change.

But resistance to later starts is less about the science than it is about logistical and financial difficulties, especially with basics like busing.

State Rep. John Ray Clemmons, a Nashville Democrat, tried to pass a bill mandating later start times in 2022.

"I'm starting to experience this with one of my own children," he said during a committee hearing on the bill. He dug into the biology, including the famous sleep hormone melatonin.

Melatonin makes people feel drowsy. The brain starts producing it when it gets dark outside, and its production peaks in the middle of the night. Adolescents' brains start releasing melatonin about three hours later than adults' and younger children's brains, according to the American Chemical Society. When teens wake up early, their brains are still producing melatonin.

"Because of the way adolescents' bodies release melatonin, waking a teen at 7 a.m. is akin to waking one of us at 4 a.m.," Clemmons said.

He brought in a local parent, Anna Thorsen, who testified that later start time legislation could protect vulnerable kids like hers.

"My youngest daughter is a freshman who suffers from a rare genetic epilepsy that killed her older sister last year," she said. "In fact, last March, my youngest daughter had a life-threatening seizure that was partially induced by sleep deprivation."

Rep. John Ragan, a Knoxville-area Republican, said almost all the feedback he heard on the bill came from Nashville.

"Go to your school board and tell them to change the rule, change the law, change their start times," he said. "But to mandate [the rest of the state] do this because of one school board that doesn’t want to listen to their parents?"

Legislative leaders gave the bill one hearing. It didn't pass into state law.

That leaves Nashville, a city that often calls itself the Silicon Valley of health care, to figure out its own path. O'Connell is now on the case. The mayor has some power over the school budget, which gives him influence in education policy. However, it's up to the school board to determine start times.

"Early start times, particularly for adolescents, are problematic," the mayor said. "We also know that making a change — even a 30-minute change — has a lot of logistics."

A major concern has been busing. Even in normal times, districts use the same buses and drivers for students of all ages. They stagger start times to do that, with high schoolers arriving and leaving school earliest in the day. The idea is that they can handle being alone in the dark at a bus stop more readily than smaller children, and it also lets them get home first to help take care of younger siblings after school.

If high schools started as late as middle and elementary schools, that would likely mean strain on transportation resources. O'Connell said Nashville's limited mass transit compounds the problem.

"That is one of the biggest issues to resolve," he said.

Several years ago, Collierville, a district in suburban Memphis, launched a study on school start times. That district serves far fewer students — 9,000, compared with Nashville's roughly 86,000.

Collierville officials estimated in the study that busing costs associated with delayed start times could be as high as $1.4 million annually. That estimate assumed the district would need more drivers, more fuel and maintenance, more storage facilities, and additional support personnel — for example, an additional dispatcher and mechanic.

Despite that, the district did push back high school start times in 2018.

O'Connell said one of the concerns he has heard from parents is financial, such as that they need help with family-run businesses or they need their students to help generate household income at other jobs after school lets out.

The National Sleep Foundation, a nonprofit that advocates for later start times, conducted a 2022 survey of parents, teachers, and other adults that found that only about one-third of the parents who responded wanted later starts. Adults as a whole and teachers responded slightly more favorably, but less than 40% of each group supported delaying the day.

A National Education Association article from 2022 found that many parents who oppose later start times don't necessarily doubt the science; they're concerned about scheduling.

Wahlstrom, the education researcher, said she fears parents underestimate how important sleep is to brain development and academic performance, especially on weeknights.

“Sometimes both parents and teens think that they can just catch up on their sleep on the weekend. That is a total false assumption," said Wahlstrom, who equated sleep to food for the brain. "It’s like, 'OK, we’re going to deprive ourselves of adequate food three days out of the week, but then we’re going to gorge on food on the weekend.' That’s not healthy."

She explained how a lack of sleep can impede scholastic success: The brain shifts memory into long-term storage during deep sleep, so missing out on that rest means retaining less material.

But — perhaps more importantly — sleep helps teenagers improve their mental health. U.S. Surgeon General Vivek Murthy has been raising alarm bells about youth mental health, noting that a third of teenagers overall and half of teenage girls have reported persistent feelings of hopelessness.

And Wahlstrom said teen sleep deprivation leads to worse mental and behavioral health, which can affect the whole family. She and her team conducted a study funded by the Centers for Disease Control and Prevention on the effects of later start times on ninth to 12th graders by surveying 9,000 students at eight high schools in Minnesota, Colorado, and Wyoming from 2010 to 2013. They found students who got at least eight hours of sleep were less likely to report symptoms of depression.

"We do know that there is greater use of drugs, cigarettes, and alcohol when a teen is getting less than eight hours," she said. "We also know that there is a significant link between teenage depression and any sleep amount that is less than eight hours.”

More than 92% of parents surveyed in a Minnesota school district as part of one of her earlier studies responded that their teenager was easier to live with after the later start time went into effect.

"Many parents have anecdotally told me that their child is a different child. They are able to speak with them at breakfast. They are chatty in the car. They don’t have moody episodes and fly off the handle," she said. "The parents are just saying it’s remarkable that this has made such a change in their child’s life and their family dynamics.”

This article is from a reporting partnership that includes WPLN and KFF Health News.