They’re sitting in the classroom, but their heads are home on their pillows.

It's a double whammy. They're not getting enough sleep to recharge their brains, and we're asking their brains to be on duty at the wrong time.

Kids are too sleepy to learn well. They're too sleepy to be happy. And they're at great risk for such things as traffic accidents.

This can put their circadian rhythm, or biological clock, in conflict with the school bell, ... The result illustrates a critical trend: too many teens come to school too sleepy to learn. And their fatigue often leads to behavior problems that contribute to a negative overall school performance and experience.

The 'why' questions are the hardest ones to answer in science.

Teen-agers don't need less sleep the older they get. They still need as much sleep as they did when they were pre-teens, ... We, as a society, are asking them to sleep at the wrong time.

When children are little, their sleep pressure rises faster so they fall asleep early, but when it's slower, like it is for teenagers, it's harder to get to sleep.