That’s too early, Wheaton says. Tweens and teens are experiencing shifts in their natural sleep cycles. Their bodies’ inner “clocks” make it hard for them to go to bed before 10:30 or 11:00 p.m. But to get to school on time, they have to wake up as early as 5:30 a.m. A first school bell just after 8 a.m. slices into the 8.5 to 9.5 hours of sleep tweens and teens need to be healthy and perform at their best, she says. “We’re fighting biology.”