Dozing at their desks

Sixteen-year-old Danny is a typically active teenager. He plays lacrosse 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 one and a half 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 rhythms - favor later bedtimes and later wake-up times.

But, with many school systems starting classes as early as seven am, 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 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.

"Any drowsy driver is dangerous, but a teenager with a lack of experience can be even more dangerous," says Breus.

Dr. Breus acknowledges that there are other factors that contribute to a teenager's sleep loss. School 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.

Later school start time equals happier, healthier teens

Dozens of school districts around the country have been looking at these studies and are considering ways to adjust their class schedules.

Eric Peterson is head of St. George's School, a private boarding school for grades 9-12 in the northeastern state of Rhode Island.

After looking at the medical research on adolescent sleep needs and observing students in his own school, Peterson decided to change his school's start time from 8:00 am to 8:30 am on a trial basis to see if a 30-minute change would make a difference.

"What was really astonishing was how many benefits and how significant the benefits were," he says. "In the research itself, we saw just over a 50 decrease in health-center admissions for fatigue, or fatigue-related illness, or rest requests. We saw almost 35 percent decrease in first-period tardiness. Students reported that they were more alert. They were less sleepy during the day."

And, according to Dr. Patricia Moss, assistant dean for Academic Affairs at St. George's School, students weren't the only ones reporting better results in the classroom. She says virtually all the teachers almost immediately noticed much more alertness in the classroom, and there was definitely a more positive mood all around.

"Kids were happier to be there at 8:30 than they were at 8:00," she says. "So our experience across the total spectrum was, universally, extremely positive and surprisingly so."

Peterson says there was another unexpected area of change when the school changed its start time.

"We saw probably a greater than 30 percent increase in student attendance at breakfast, and of the food that they were eating. We more than doubled the amount of milk, eggs, fruit and cereal. So it was quality breakfast foods that the kids were eating. So they were better fueled as well as better rested."

Ross and Peterson acknowledge that making schedule changes has been easier at a small, private boarding school than it might be for the larger US public school system. But they are hopeful that others will find a way.

"In the end," says Peterson, "schools ought to do what's the right thing for their students, first and foremost, and this element of the program is very clear - certainly for us as a school - but I think as a general example to other schools, is pretty compelling, and so I would argue that it's worth doing."

In the meantime, experts say that - as we learn more about adolescent sleep patterns and exactly why they need those nine hours of sleep - it is up to families and individual students like Danny to take personal responsibility for paying more attention to sleep as an essential element of a healthy life.

lacrosse: a game played on a field by two teams of ten players who use sticks with curved nets on them to catch, carry, and throw the ball 长曲棍球（两队各十名队员，用带网兜的球棒接球、带球和传球）

circadian: connected with the changes in the bodies of people or animals over each period of 24 hours （指每 24 小时人或动物体内变化）昼夜节律的，生理节奏的

cranky: bad-tempered 脾气坏的

tardiness: （行动）缓慢；拖拉；迟缓

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（来源：VOA 编辑：陈丹妮）