Many parents know the scene: The groggy, sleep-deprived teenager stumbles through breakfast and falls asleep over afternoon homework, only to spring to life, wide-eyed and alert, at 10 p.m.—just as Mom and Dad are nodding off.

Fortunately for parents, science has gotten more sophisticated at explaining why, starting at puberty, a teen's internal sleep-wake clock seems to go off the rails. Researchers are also connecting the dots between the resulting sleep loss and behavior long chalked up to just "being a teenager." This includes more risk-taking, less self-control, a drop in school performance and a rise in the incidence of depression.

Few parents realize that the common practice of letting teens set their own bedtime can fuel further mutations in the biological processes that knocked them off track. Sue Shellenbarger and Brown University's Dr. Mary Carskadon discuss details on Lunch Break.

One 2010 study from the University of British Columbia, for example, found that sleep loss can hamper neuron growth in the brain during adolescence, a critical period for cognitive development.

Findings linking sleep loss to adolescent turbulence are "really revelatory," says Michael Terman, a professor of clinical psychology and psychiatry at Columbia University Medical Center and co-author of "Chronotherapy," a forthcoming book on resetting the body clock. "These are reactions to a basic change in the way teens' physiology and behavior is organized."

Despite such revelations, there are still no clear solutions for the teen-zombie syndrome. Should a parent try to enforce strict wake-up and bedtimes, even though they conflict with the teen's body clock? Or try to create a workable sleep schedule around that natural cycle? Coupled with a trend toward predawn school start times and peer pressure to socialize online into the wee hours, the result can upset kids' health, school performance—and family peace.

Jeremy Kern, 16 years old, of San Diego, gets up at 6:30 a.m. for school and tries to fall asleep by 10 p.m. But a heavy load of homework and extracurricular activities, including playing saxophone in his school marching band and in a theater orchestra, often keep him up later.

"I need 10 hours of sleep to not feel tired, and every single day I have to deal with being exhausted," Jeremy says. He stays awake during early-afternoon classes "by sheer force of will." And as research shows, sleep loss makes him more emotionally volatile, Jeremy says, like when he recently broke up with his girlfriend: "You are more irrational when you're sleep deprived. Your emotions are much harder to control."

Only 7.6% of teens get the recommended 9 to 10 hours of sleep, 23.5% get eight hours and 38.7% are seriously sleep-deprived at six or fewer hours a night, says a 2011 study by the Centers for Disease Control and Prevention.

It's a biological 1-2-3 punch. First, the onset of puberty brings a median 1.5-hour delay in the body's release of the sleep-inducing hormone melatonin, says Mary Carskadon, a professor of psychiatry and human behavior at the Brown University medical school and a leading sleep researcher.

Sleep Tech for Teens

When adolescents stay up late, it's often because they're welded to their gadgets. Here are three that might actually ease their way to dreamland.

  • Philips Wake-Up Light. Teens could wind down to its gradually dimming evening glow, then awaken to a gradual rise in light and nature sounds— especially good for dark winter mornings. Includes digital clock and AM/FM radio. $100 at
  • Sleepsonic Stereo Speaker Pillow. With built-in digital stereo speakers, this could help music-loving teens drift off without the discomfort of headphones; $140 and up at
  • F.lux. This computer-screen app gradually dims the most stimulating light wavelengths, helping teens wind down while finishing homework; free at

Second, "sleep pressure," or the buildup of the need to sleep as the day wears on, slows during adolescence. That is, kids don't become sleepy as early. This sleep delay isn't just a passing impulse: It continues to increase through adolescence, peaking at age 19.5 in girls and age 20.9 in boys, Dr. Carskadon's research shows.

Finally, teens lose some of their sensitivity to morning light, the kind that spurs awakening and alertness. And they become more reactive to nighttime light, sparking activity later into the evening.

Dr. Carskadon says letting teens set their own schedules can lead to a downward spiral. Teens left to their own devices tend to cycle later, soaking up stimulating light from their computers. This can further delay sleep by 2½ to 3 hours.

Many parents feel defeated by schools' early start times. More than half of public high schools start before 8 a.m., according to a 2011 Brookings Institution study.

Maya Zimmerman's first class is at 7:20 a.m., and "when I wake up in the morning, I literally want to die," says the 16-year-old Falls Church, Va., high-school junior. "I feel like it's the middle of the night and I don't feel like eating cereal." Ms. Zimmerman says she battles fatigue in class and often nods off while doing homework after school.

More than 35 schools or school districts in at least 21 states have delayed start times in recent years to allow teens to sleep longer, according to reports gathered by advocates. In Wake County, N.C., where school start times were changed several times over a seven-year period, a one-hour delay was linked to an increase of three percentile points in middle-school students' math and reading scores, according to a study published earlier this year in the Economics of Education Review.

Many schools, however, have rejected parental pressure to delay school starts, citing bus-cost savings, or the need to keep afternoons open for teens' sports or other activities.

Sleep loss is linked in research to decreases in memory, attention and academic performance. Impaired functioning of the prefrontal cortex, which helps regulate sleep, has been detected in youngsters with attention deficit hyperactivity disorder.

Sleep-deprived teens are more likely to feel sad or hopeless, or to seriously consider suicide, according to a 2011 study by the CDC. A study published earlier this year by Dr. Carskadon and others links sleep deprivation in college freshmen to the expression of genetic factors linked to depression.

Still, most teens resist parents' setting bedtimes. Peer pressure plays a role. Teens with a friend who sleeps less than seven hours a night are 11% more likely to sleep less than seven hours themselves, says a 2010 study in the science journal PLoS One.

Claude Albertario of Oceanside, N.Y., says his 15-year-old daughter Rianna stays up much too late, leaving her TV on through the night, "no matter my yelling." Rianna says she isn't sleepy until after midnight and usually falls asleep at 1 a.m. or 1:30 a.m., just five hours before she has to get up for school. She claims her TV helps her sleep by masking nighttime noises around the house.

An argument that does work with Rianna: Citing research linking sleep loss in teens to obesity and other health problems. Knowing that more sleep will help her keep her skin clear and avoid gaining weight "motivates me more," says Rianna, who is trying gradually to move her bedtime up to midnight.

Write to Sue Shellenbarger at