CHICAGO (CBS) — Any parent with teenagers will tell you, their kids can’t get up in the morning.

So, why are they always tired?

Experts blame their biological clocks, school schedules, and as CBS 2’s Mary Kay Kleist reports, even cell phones.

It’s a slow-go every morning for 17-year old John Pelka.

“In the beginning of the day, I’m definitely dragging. I’m definitely in a bad mood,” Pelka said.

His mother Geralyn Pelka said, “He’s just exhausted. And then he’s using caffeine in the morning. He can’t really get going.”

Medical experts say teens need about 9 hours of sleep every night. But teens we talked to say that never happens.

Pelka said, “I don’t get 9 hours, I usually get 6 or 7.”

High school student Stephanie Nowak said, “I’m up at 6. Yeah, I don’t get that much sleep.”

Another high school student Janet Hsueh said, “It usually takes like 3 alarm clocks to get me up.” And one reason might be cell phones.

A Pew internet survey found that 86 percent of older teens sleep with their cell phones. But technology is just one factor keeping kids awake, the other, experts say is biological. Their body clocks are wired to stay up later and sleep in. But with current school schedules, that’s impossible.

Dr. Phyllis Zee from Northwestern University Feinberg School of Medicine cautions a sleep deprived teen could develop health issues.

“Irritability, maybe even mood changes, and depression, which is also on the rise for our teenage population,” Zee said. “And more recently the data does show that it can actually affect your weight, and the risk for obesity.”

If kids try to make up the sleep on weekends, it can make them even more tired on monday morning. Stephanie Crowley, Ph.D. from Rush University Medical Center says she’d like to see school start later for teens to accomodate their biological clocks.

“Trying to sleep at the right time for your brain is ideal,” Crowley said.

A recent study found that delaying school start times to 8:30 a.m. resulted in teenagers getting an hour of additional sleep. The students reported feeling less depressed and more motivated.

John Pelka’s high school starts at 7:45 and he has to catch the bus an hour before that. Some mornings he barely makes it.

His mother Geralyn said, “It would be wonderful if school started later, for both of us.” Schools we called told us that early start times are due to bus and athletic schedules.

Medical experts say if your teen has a tough time falling asleep, consider cutting off electronic devices one hour before bed or keeping cell phones out of the bedroom at night. Limit caffeine in the afternoon and evening. Also, try to keep them on the same sleep schedule on the weekends — if they’re sleepy, have them take an afternoon nap.