About half American teenagers do not get enough sleep on school nights.They get an average of sixty to ninety minutes less than experts say they need. One reason for _ is biology.Experts say teens are biologically programmed to go to sleep later and wake up later than other age groups.Yet many schools start classes as early as seven in the morning.As a result,many students go to class feeling like sixteenyearold Danny.He is an active teen-- except in the morning."Getting up in the morning is pretty terrible.I'm just very out of it and tired.Through the first and second period I can hardly stay awake," he said. Michael Breus is a psychologist.Teens,he says,need to sleep eight to nine hours or even nine to ten hours a night.He says sleepy teens can experience a form of depression  that could have big influence on their general well being.It can affect not just their ability in the classroom but also on the sports field and on the road.So what can schools do about sleepy students?The psychologist says one thing they can do is to start classes later in the morning.Studies show that students can improve by a full letter grade in their first and second period classes. Eric Peterson is the head of St.George's School in the northeastern state of Rhode Island.He wanted to see if a thirtyminute delay would make a difference.It did.He says visits to the health center by tired students decreased by half.Late arrivals to the first period fell by a third.And students reported that they were less sleepy during the day.Eric Peterson knows that changing start times is easier at a small school like his.But he is hopeful that other schools will find a way. What can we infer from the passage?
Danny is a lazy boy and always late for school. Teens should go to bed early and get up early, too. The psychologist has no idea how to solve the problem. Enough sleep makes a healthy and active student.