据调查，一半的美国学生缺少睡眠，每个上学的日子都缺少1.5个小时的睡眠时间。这些睡眠缺少的问题除了学业压力之外，很大程度上也是由于美国学生的课外娱乐活动导致的。

（小编不由联想到中国学生们。美国学生都缺少睡眠，让我们披星戴月的中国学生情何以堪啊！）

Most American teenagers are missing up to 1½ hours of sleep every school night.

About 50 percent of American teenagers are not getting the sleep they need during the school year, according to a poll by the National Sleep Foundation.

Experts say that teens are biologically programmed to go to sleep later and get up later than other age groups, which makes their body's natural rhythm incompatible(互不相容) with early school hours. And this sleep deficit is having negative consequences on almost all facets of teens' lives.

Now, an increasing number of educators are trying to reconcile(使一致) the sleep needs of their teenage students with the practical realities of earlier school schedules.

Sixteen-year-old Danny is also part of a growing number of teenagers who are sleep deprived.

Dozing at their desks

Sixteen-year-old Danny is a typically active teenager. He plays lacrosse(长曲棍球) and football and likes listening to rock music. But Danny is also part of a growing number of teenagers who are sleep deprived.

"Getting up in the morning is pretty terrible," he says. "I'm just very out of it and tired. And then, going to school, I'm out of it. And through first and second period [classes], I can barely stay awake."

Danny is not alone. Surveys show that half of all teenagers in the country are missing an average of one to 1½ hours of sleep every school night, and that's having negative consequences on their performance - in and out of the classroom.

While some believe that a teenager's reluctance to get up in the morning is sheer laziness, sleep experts say that's not necessarily the case. Michael Breus, a clinical psychologist who specializes in sleep disorders, says kids like Danny aren't just a bunch of lazy kids.

"These are children whose biological rhythms, more times than not, are off," says Breus.

Negative consequences

Teenager's biological rhythms - often referred to as their circadian(日夜规律) rhythms - favor later bedtimes and later wake-up times.

But, with many school systems starting classes as early as seven a.m., teenagers like Danny often come to school half asleep. And that, says Breus, has consequences.

 "We have long known that the more sleep deprived you are, the more cranky(暴躁) you are. So when your child, who really needs eight or nine hours, is only sleeping for seven hours a night, they are going to experience a form of depression that could be significant and could have some pretty major effects on their overall well-being."

According to Breus, that mood-altering deficit can affect a teen's academic performance, their athletic ability and even their performance behind the wheel of a car.

"We know that drowsy(昏昏欲睡的) driving is of utmost concern because these are kids who haven't had a tremendous amount of experience in driving to begin with.”Any drowsy driver is dangerous, says Breus, but a teenager with a lack of experience can be even more dangerous.

He acknowledges that there are other factors that contribute to a teenager's sleep loss. Twenty-four-hour access to the Internet and fast-paced video games are tempting products in the digital age. And the proliferation of caffeinated drinks is also wreaking havoc(造成破坏) with our children's natural body rhythms. But school, says Breus, is one area where small changes can bring about dramatic results.

"There've been multiple research studies that now show that in fact when you change the school start time, allowing children to start later in the morning, their grades go up by almost a full letter grade in their first- and second-period (classes)," he says.