Washington ? There are nights when Jane Hopkins feels like a sleep cop.

She will climb out of her bed in the wee hours to see whether her teenage sons are really asleep. If she spies them still awake, playing on the computer or the PlayStation3 in the basement of their College Park home, she will insist: It’s time for bed. It was time hours ago.

“If you find the perfect child who goes to bed early, will you let me know?” she asks.

Pushing teens to get enough rest is an ever-more difficult quest as another school year begins and triggers another round of family debates about cell phones and game consoles, iPods and laptops. What teen wants to drift off when another text is arriving, when X-Box friends are still online, when Facebook is 24/7?

The abundance of digital diversions has only amped up the usual tug-of-war between generations about when the lights go out, and worried parents can lose sleep just trying to keep up. “I’m tired,” Hopkins, 47, says one recent day, having risen to find her sons awake at 1 a.m.

Experts say 80 percent of adolescents don’t get their recommended sleep, about nine hours, and the effects are nothing to yawn about.

But getting teenagers into bed — despite piles of homework and the lure of socializing through cellphones and cyberspace — can be tough, and Judith Owens, a sleep researcher at Brown University’s Alpert Medical School, says many parents “don’t know what time their kids go to bed, because they are not staying up for it.”

Owens quotes a poll by the National Sleep Foundation, which shows 90 percent of parents think their teens get enough sleep at least several nights a week, revealing what researchers see as a striking “awareness gap.” More sleep cops would be better, she argues — or at least rules that get teens in bed by, say, 10 or 11 p.m.

“There’s definitely a disconnect,” she said.

Experts say the math of teen sleep is improbable — with super-early starts to school days, with so many activities packed into teen lives, with the circadian rhythms of adolescents leaving many unable to get to sleep before 11 or midnight.

Add to that: texting and Facebooking and gaming.

“Our teens have an overwhelming need for sleep and an insurmountable series of obstacles they have to navigate in order to find a quiet place and time to get to sleep,” says Helene Emsellem, author of “Snooze … Or Lose!” and director of the Center for Sleep & Wake Disorders outside Washington, where the appointment schedule is especially busy this time of year.

She and other experts see lack of sleep as a serious problem, with studies showing links to lower school performance, reduced cognitive abilities and mood problems, including depression.

A Pew Research Center study released in April showed that more than four of five adolescents say they have slept with their cellphones in or near their bed. Some wake every time their phones buzz with a new text message. Some young couples text through the night.

To ward against this, some parents ban the devices after a certain hour — insisting cellphones get handed over at 9 p.m., for example, or that they are placed on a parent’s dresser before bed.

But at school, sleepy faces are a fact of life.

“It’s not just the tired thing, but they are zoning out in class,” says James Fernandez, principal of Albert Einstein High School in Kensington, Md. “It’s a big problem. And if you get a substitute in the classroom, they all go to sleep; it’s looky here, a 40-minute nap.”

The sleep mandate can get a little less clear when teenagers are staying up to do their homework.

Should a parent shoo them to bed?

In Clarksburg, Md., Lisa Winstel, 47, says her daughter stays up to read, so in a sense she shouldn’t complain. But lately the 13-year-old is still turning the pages of her novels at 1 a.m. When Winstel gets up to insist the lights must go out, the noise sets off a chain reaction.

Her 6-year-old son wakes up. Her dog wants go outside. And by the time Winstel is back under the covers, her night’s sleep of seven hours or less is shorter still.

Who said only parents of newborns are bleary-eyed?

“I think parents are, by and large, sleep-deprived,” she says.