It is hardly a revelation that teenagers like to sleep late. But more and more research is showing that this is not just a preference  or even the result of late-night studying or instant messaging  but is rooted in their biological rhythms. All of this would be little more than an interesting observation except that most high schools start so early, and so many teenagers are having a hard time staying awake.

A recent Op-Ed article in The Times cited a National Sleep Foundation survey in which more than a quarter of the students reported that they fell asleep in class at least once a week. Researchers say this is true because youngsters  beginning around age 12 until they reach their mid-20s  only start producing melatonin, the sleep-inducing hormone, around 11 p.m. and that production peaks until about 7 a.m. In adults, melatonin peaks until around 4 a.m. Trying to wake up a teenager before 7 o’clock is like trying to awake an adult before 4 a.m.

The obvious remedy would be for high schools to start later  well after 8 a.m. A handful of schools that have switched have reported beneficial results. School officials in Minneapolis say that attendance improved and students’ grades rose slightly after they changed to an 8:40 a.m. start several years ago. In Wilton, Conn., where the high school start time was pushed back to 8:20 a.m. from 7:35, teachers and parents reported improved student behavior and greater alertness. Surveys of students in both districts indicated that they did not use the later starts as an excuse to go to bed later.

Numerous districts have considered the idea of later high school hours, only to drop it because of fierce adult opposition. Coaches complain that the later classroom hours in the afternoon would take time from their training programs and teams’ success. School bus companies would be forced to change their schedules. And many parents complained that they would have to adjust their own schedules.