While teens' daily sleep requirements do decline somewhat, they also naturally begin going to bed later. "It isn't just bone-headedness, it's biology," says Gromer. But this normal tendency can spell trouble if high school hours start earlier than what teens are used to. And when teens' sleep needs and a shifting sleep schedule are combined with a packed activity schedule, it can cut into the amount of healthy sleep they’re getting. Factor in their tendency to wake up later in the morning on weekends, and it can add up to frustration for parents trying to get their teens on a healthy sleep schedule.