Across the nation, officials are delaying middle and high school start times. The reason: So teens have a better shot at getting the sleep they desperately need.

Among districts that are considering the issue is the Owen J. Roberts School District in northern Chester County.

To help inform the decision, sleep specialist Wendy M. Troxel will give a presentation from 6:30 to 8 p.m. Nov. 20 at the middle school, 901 Ridge Rd., Pottstown. It is open to the public.

Troxel, who has a doctorate in clinical and health psychology, is a senior behavioral and social scientist at the RAND Corp. and an adjunct faculty member in psychiatry and psychology at the University of Pittsburgh.

She was an advisory member of Pennsylvania’s Joint State Commission on Secondary School Start Times, which in October issued a report concluding that the optimum starting time for secondary school is 8:30 a.m. or later. The report stopped short of calling for a statewide policy.

Troxel recently spoke to us about the science behind teen sleep.

If kids aren’t getting enough sleep, why don’t they just go to bed earlier?

The issue is a biological one. Teenagers experience a delay in their biological rhythms, which determines when we feel awake or when we feel sleepy. Their circadian rhythms are about two hours later than that of adults and younger children.

We don’t know precisely why, although we do know the mechanism. The release of the hormone melatonin is about two hours delayed in teenagers. Melatonin is the hormone of darkness. It tells the brain it’s time to go to sleep. Teenagers’ melatonin release happens around 11 p.m., two hours after their parents’. You can’t just tell kids to go to bed at 9 p.m. if their brains aren’t ready for it. It’s not like it’s a willful preference. It’s similar to jet lag. Literally, teens do not get the biological signal to allow them to fall asleep.

What is the recommended amount of sleep for a teen, and how many kids get that?

The recommendation is eight to 10 hours, more than what’s recommended for adults. Adolescents aren’t just mini-adults. They are still in a dramatic developmental period and they need more sleep. The Centers for Disease Control and Prevention says only about a quarter of adolescents get eight hours, which would be a bare minimum. We consider 9¼ hours to be optimum, but only about one in 10 teens gets that.

What are the effects of not getting enough sleep?

About one in five teenagers regularly falls asleep in class, which is a real threat to their ability to learn. So, not surprisingly, teens who don’t get enough sleep show poor academic performance with lower grades, lower standardized test scores, even poorer graduation rates.

Sleep loss is directly related to mental and behavioral health problems. There are strong links between sleep loss and depression, suicidal thoughts and behaviors, and risk-taking behaviors, such as drinking alcohol or taking drugs, plus sexual risk-taking.

Sleep, in general, is associated with memory and learning. Also, most of our rapid eye movement sleep — dream sleep — occurs later in the sleep cycle, which for teens is in the morning, right when we’re waking them up. We know that dream sleep, or REM sleep, is critically important for learning, memory consolidation, and emotional processing. It’s been said that sleep acts as overnight therapy, where you process the things that happened during the day. When we deprive teens of REM sleep, we’re reducing the opportunity for them to deal with those emotions that we know are so difficult for kids.

There are also physical health consequences. Teens who don’t get enough sleep are more prone to athletic injuries. They are also at higher risk for obesity. On an even broader level, sleep loss in teens is a public safety issue. Young drivers, from ages 16 to 24, account for about 50% of drowsy-driving crashes.

Does an hour really make a big difference?

An hour has profound effects. Even an extra half-hour of sleep can make a difference. Plus, if you add 30 minutes per night across the course of a week and a school year, that’s a lot of added sleep time.

The data show many positive benefits associated with changing to later school start times. The first is that in fact, teens do get more sleep when schools start later. Many people assumed that kids would just stay up later. But that’s not what the data shows. It shows that teenagers’ bedtimes stay roughly the same. But their wake-up times get extended. It results in more sleep and more REM sleep.

The second is that there are academic benefits. This is most strongly seen in a reduction in tardiness rates and absenteeism. When teens show up for school on time and they are more well-rested, ready to learn, that also relates to graduation rates. There is also data to show that standardized test scores go up by two to three percentage points.

Car crash rates, in general, go down in districts with a delayed start time.

What are the most common misconceptions about changing school start times?

There’s this idea that we’re just coddling our teens. That we somehow need to prepare them for the “real world” by depriving them of sleep. It doesn’t make sense. Should we starve our children to prepare them for the real world? Sleep is a fundamental biological need.

Some people express concerns about the impact on sports if schools get out later. We have research to counter this argument. In districts that have delayed school start times, they have gone on to win state championships. One study showed that, if anything, there was more participation in extracurricular activities, not less. It makes sense. When you have well-slept teens, they are more engaged, they are better athletes.

Finally, there is the reaction that it’s just too expensive. This is not borne out by the data. My RAND colleagues and I published an economic analysis showing what would happen if there was a nationwide shift to 8:30 a.m. — the costs and the benefits.

What we found was that over a 10-year period, the U.S. economy would see an $83 billion boost. That economic gain would be driven by the reduction in car crash rates and improved learning and graduation rates, which lead to higher college rates and an increase in subsequent lifetime earnings.

We recognize there are concerns about the costs. There may need to be changes in bus routes. Lights may need to be added to athletic fields. Even at that, we found that most states across the country would reach the break-even point in about two years.