Sleep deprivation seems to start early. A 2004 survey by the National Sleep Foundation found that on average, children in every age group from infancy through fifth grade failed to get even the low end of the recommended range of sleep.

The real agony emerges in adolescence. As children go through puberty, two things happen to make getting enough sleep problematic: they need more sleep than prepubescent children, not less — 9 to 10 hours a night — and their body clocks shift to a later time to fall asleep and, consequently, a later awakening.

Amy R. Wolfson, a psychologist at the College of the Holy Cross in Worcester, Mass., and Mary A. Carskadon, a sleep researcher at the Brown School of Medicine in Providence, R.I., have found that few adolescents sleep the amount they need. The average eighth grader sleeps less than eight hours, and more than a quarter of high school and college students are chronically sleep deprived, they reported.

In a report last February in the journal Pediatrics, researchers from the Columbia University School of Nursing estimated that “15 million American children are affected by inadequate sleep.” They based this on the findings of a national health survey in 2003 of 68,418 children ages 6 to 17. In the study, by Arlene Smaldone and colleagues, the percentage of children who failed to sleep enough rose with age and increased markedly among children 12 and older.

Sleep deprivation has been linked to poorer grades, moodiness and depression. Though you may question which comes first, Avi Sadeh, a psychologist at Tel Aviv University, studied the effects of adding or subtracting one hour of sleep on 77 children in the fourth and sixth grades. Those deprived of an hour’s sleep performed less well on tests for reaction time, recall and responsiveness than the children who slept the extra hour.

Insufficient sleep in the teenage years has been associated with increased risks of disciplinary problems, sleepiness in class and poor concentration, not to mention traffic accidents.

With televisions and computers in their rooms, many teenagers cannot resist the temptation to stay up late, especially because their bodies do not begin to produce the sleep hormone melatonin until 1 a.m., as opposed to 10 p.m. in most adults.