Summer nights. No homework. Late night TV and midnight movies. No fixed bedtime.

That free and easy schedule is changing soon, as the start of school approaches.

Families should start adjusting their bedtime sleep routines so that kids’ internal clocks are back on track for the school routine.

Doctors with Baptist Hospital, Miami Children’s, Joe DiMaggio Memorial and the University of Miami all agree: Good sleep is key for students’ health and academic success.

“Sleep is actually critical for learning and memory. Sleep is critical for growth,” said Dr. Marcel Deray, director of the sleep disorders center at Miami Children’s Hospital.

During sleep, the body produces growth hormones. Research shows that people who don’t get enough rest are more likely to be overweight and can’t fight off infections as much. There is also a correlation between sleep apnea, which can disrupt sleep, and hyperactivity, Deray said.

So since sleep is so important, how can parents get their kids — especially teenagers — up early for school?

Start getting back on schedule soon, about a week or two before the first day of school, doctors say.

For younger school-age children, doctors suggest parents be firm with bedtime, keep a regular bedtime schedule and limit TV and computer activity.

“Sleep is like eating,” Deray said. “You can’t wait until they’re tired to establish their bedtime, just like you don’t wait for them to be hungry to feed them.”

Some doctors, like Dr. Juan Martinez with Joe DiMaggio, also recommend having kids sleep in their own rooms, and not with their parents, so that everyone gets rest. “It’s really important to get enough sleep and enough quality sleep,” he said.

For teenagers, like so many things in life, it’s more complicated.

Physiologically, they need a lot of sleep — 9 or even 10 hours — because of their growth and hormonal changes, said Dr. Kunjana Mavunda, a pediatric pulmonologist with Baptist Health. They also naturally have a different internal clock, or circadian rhythm, that delays their natural bedtime and makes them more night owls and more inclined to sleep in. That biological clock clashes with school’s early morning bell. High schools start at 7:30 a.m.

Mavunda, who conducts studies on children at the hospital’s sleep center, worries the most about teenagers when it comes to sleep. Muvanda said during the week, many teens get sleep deprived and try to catch up on the weekend. Problems concentrating in class, behavior issues, angry episodes and hyperactive antics are no surprise. “This is a societal problem that hasn’t been dealt with,” she said.

Tips for teenagers and sleep:

• Stop staying up late as school starts.

• Don’t watch TV, play video games or surf online an hour before bedtime.

• Cut back on texting.

• Keep electronic lights out of the bedroom.

• Avoid strenuous activity a couple of hours before bedtime. Try reading a book or doing omething else relaxing.

• Gradually start getting up earlier, in roughly half-hour increments, so the first day is not a shock.

Dr. Shahriar Shahzeidi, an assistant professor of pediatrics at the University of Miami and member of the UHealth sleep medicine program, advocates a later start-time for high schoolers.

But absent a policy shift, he said melatonin can help teens ease into sleep earlier. Melatonin is a natural hormone released by the body; it is available at drugstores as a supplement.

Shahzeidi said his 16-year-old daughter takes melatonin about 15 minutes before bedtime. Bright lights in the morning help wake her up.

“That helps her a lot. The sleep frame moves a little bit forward and she can actually adjust her life around it.,” he said. “At 8:30 she takes the melatonin and goes to sleep at 9. Then she can wake up at 6 in the morning and she’s had enough sleep.”

Another doctor with teenage children, Martinez with Joe DiMaggio Hospital, said his sons have started to wake up a half hour earlier. Martinez said every three days, he tries to move the wake-up up another half hour. In the summer his three teenage sons sleep until 10 or 11 in the morning.

“In a couple of weeks, they’re going to hear the 6 a.m. alarm and they’ll have to get ready for school and have some semblance of being awake in class,” Martinez said.

He advised parents to talk with their teenagers, be patient and explain the importance of sleep. That can help keep bedtime from being a sore spot.

“Not only are we battling against staying up late, video games, TV, etc., we also have to battle the normal phenomenon of their bodies wanting to stay up a little later.”