• Mayo Clinic Minute: How much sleep do kids need?

As children across the country head back into the classroom, now is the time to start easing them back into a normal sleep schedule. How much sleep kids need to maximize their learning potential depends partially on their age. But the key to getting them on a regular schedule may have more to do with what time they wake up than what time they go to sleep.

Watch: The Mayo Clinic Minute

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It's one of the most important keys to their success, but as kids are heading back to school, too many of them aren't getting enough sleep.

Suresh Kotagal, M.D., a pediatric neurologist at Mayo Clinic, says younger kids should be getting at least eight to nine hours of sleep every night, while teenagers can get by on seven-and-a-half to eight-and-a-half.

"That would be the ideal for ensuring optimum level of alertness during the day," Dr. Kotagal says.

Getting exercise every day also is important for a child's alertness and sleep quality.

And while Dr. Kotagal says it's probably OK for kids to be a bit lax about their sleeping habits during the summer, they should start a gradual shift back to a normal sleep schedule about two to three weeks before school starts. That gradual shift should focus on wakeup time

"If we have a fixed morning wakeup time, the bedtime itself will take care of itself," Dr. Kotagal says. "So, I think just having a fixed morning wakeup time seven days a week is a good idea."

That means even on the weekends, kids shouldn't sleep in too late.