Health Journal: Doctors probe why it's hard for many kids to get up

Health Journal: Doctors probe why it's hard for many kids to get up: "DSPS is believed to be the result of the body's internal clock -- called the circadian system -- getting stuck in the wrong place, causing kids to stay up late. As kids enter puberty, circadian rhythms that affect sleep begin to change, which is why most kids' bedtimes shift about an hour later as they get older. But for reasons no one understands, some kids experience more dramatic changes as their internal clocks shift forward too far. Those kids can't fall asleep until the early hours of the morning, but still have to get up early for school, so they have to get by on just a few hours of sleep each night."