Schools and the rest of society need to pay attention to the different sleep needs of teenagers.

A brain doctor says that making teens go to school in the morning is cruel.

The way we sleep changes with age, just like it does for other organisms. Many research have shown this. When puberty starts, kids stay up later and go to bed later. For women, this tendency lasts until age 19.5 and for males, until age 21. Then it turns around. At age 55, we awaken about the time we did before puberty. This is often two hours sooner than when teenagers are. As a result, a teenager’s 7 a.m. alarm is similar to a person in their 50s’ 5 a.m. start.

But biology is not the only problem. Other factors include parents who aren’t as strict about bedtimes, a general lack of respect for the importance of sleep, and easy access to TVs, DVDs, PCs, gaming devices, cellphones, and other devices that keep kids awake and cut into their sleep time.

The amount of sleep teenagers get varies by country, region, and social class, but all studies show that because schools start so early, they are going to bed later and not getting as much sleep as they need.

In the US, the fact that teenagers sleep later than adults because of how their bodies work led some schools to delay the start of the school day. Kyla Wahlstrom at the University of Minnesota looked at the effects and found that both academic performance and attendance were better. Both sleeping in class and self-reported depression went down.

Sleep is a biological need that improves creativity, productivity, mood, and interpersonal skills rather than being a luxury or pleasure.

If you need an alarm clock or a parent to get you out of bed, if it takes you a long time to wake up, if you feel sleepy and irritable during the day, or if you act too quickly, you probably don’t get enough sleep. Get in charge. Make sure your bedroom is dark and not too hot. Don’t text, use a computer, or watch TV for at least 30 minutes before you try to sleep, and stay away from bright lights. Try not to take naps during the day, and look for natural light in the morning to move your body clock and sleep patterns to an earlier time. After lunch, stay away from caffeine-containing beverages.