last up to 24.7 hours. Their longer day makes it even easier for them to sleep late in the morning, especially when they’re sleep deprived.

All of this means trouble for teens. Because their day-night cycle doesn’t follow the typical 24-hour clock, they don’t make the day-night shift when everyone else does—their morning comes later and their day lasts longer. And because they typically need to follow the schedule adults adhere to, they feel out of whack and are always trying to cram a longer day into a 24-hour period—and suffering the consequences. Alterations of the three sleep-wake factors—the slower buildup of sleepiness during the day, the delayed influence of light, and the longer day—make our adolescents different and uncomfortably out of sync.

Teens’ sleep phase shift desynchronizes them from the 24-hour day that the circadian rhythm is entrained, or geared, to—in other words, it upsets the balance between teens’ timing for sleeping and waking and the timing of what’s going on in their environment. And as they progress through puberty and go to sleep later and later, becoming sleep deprived from having to get to school so early in the morning, they desynchronize even further and become true night owls. Without intervention and treatment to put teens back in sync, their circadian

Physiologic and social pressures resulting in a restricted total sleep time.