Homeroom Zombies

As the school year kicks off, parents are once again struggling to cajole and, if need be, drag their exhausted teens out of bed. Later, teachers get a close-up view of sleep deprivation's effects, as bleary students zone out and even doze off in class. "I've learned never to dim the lights, even to show a video," says Lauren Boyle, a history teacher at Waltham High School in Massachusetts. "If I do, there are days when a third of the class falls asleep."

That image may make you laugh, but lack of sleep is no joke. Adolescents who don't get enough rest have more learning, health, behavior and mood problems than students who get at least nine hours a night. In some cases, teens may be incorrectly diagnosed with ADHD when sleep deprivation is actually the source of their symptoms. Perpetual lack of sleep is tied to diabetes, heart disease, obesity, depression and a shortened life span in adults, underscoring the importance of establishing good sleep habits early in life. Lack of sleep can be especially deadly for teens; car accidents are the leading cause of death among adolescents, and safety experts believe drowsy driving is a major factor.

Unfortunately, few adolescents get the sleep they need. In one recent study, researchers at Case Western Reserve University found that more than half of students slept seven hours or less, and almost one in five got less than six hours. In a survey of middle- and high-school students, University of Colorado researchers found that 82 percent said they woke up tired and unrefreshed, and more than half had trouble concentrating during the day at least once a week.

Blame multitasking for some of this. Many students are juggling after-school activities, homework and part-time jobs. Even when they manage to fulfill these obligations by a reasonable hour, television, the Internet, videogames, phone calls and text messages to friends often keep them awake deep into the night. (On average, 12th graders have four major electronic devices in their bedrooms.) Taking caffeinated soda and energy drinks late in the day and going to late-night parties on weekends add to sleep debt.

Biology also works against adolescents' sleep. The body's internal clock, which controls when a person starts to feel tired, shifts after puberty, making it hard for most teens to fall asleep before 11 p.m. Class usually begins before 8:15 a.m., with many high schools starting as early as 7:15 a.m. To get to school on time, most teens have to get up by 6:30 a.m., guaranteeing they'll be sleep-deprived during the week. Teens often sleep much later on weekends to catch up, making it even harder to fall asleep on Sunday night and wake up Monday morning. Playing catch-up on weekends also doesn't help teens stay alert when they need it most: during the week at school.

Since the 1990s, middle and high schools in more than two dozen states have experimented with later school start times. The results have been encouraging: more sleep, increased attendance, better grades and fewer driving accidents. For example, ninth graders' daily attendance rose from 83 percent to 87 percent and overall grades went up slightly when Minneapolis high schools moved the start time from 7:15 to 8:40 a.m. And car crashes involving teen drivers fell 15 percent when high schools in Fayette County, Ky., switched the high- school start time from 7:30 to 8:30 a.m. But most schools still start early, meaning teens have their work cut out for them if they want to get enough sleep.