Two new studies contribute to the body of research supporting the idea that getting enoughrest helps children at school.

The research, released Saturday in the journal Sleep,is timely, as children try to get back into the school routine and theirsleep patterns changeas they adjust from late nights and leisurely mornings to earlier bedtimes and rise-and-shine wake-up calls.

Dr. Jacques Montplaisir of the Sleep Disorders Centre at Sacre-Coeur Hospital in Montreal and his colleagues tracked close to 1,500 children from five months to six years of age, and their findings suggest that youngsters who got less sleep were more likely to have behavioural and cognitive problems in the classroom.

"The results of the paper highlight the importance of giving a child the opportunity to sleep at least 10 hours a night throughout childhood, especially before the age of 3½ years, to ensure optimal cognitive performance" in school, Montplaisir said in a statement.

And a study by Jan Van den Bulck in Leuven, Belgium, looked at teenagers — and found that the use of cellphones for calling and text messaging after lights out was prevalent. Only 38 per cent of the more than 1,600 teens studied said they never used their mobile phone after going to bed.

The study had several limitations—for instance, it relied on self-reported data — but suggests even moderate use of a cellphone after lights out raises the risk of long-term fatigue.

More sleep means better grades

Dr. Colin Shapiro of the Youthdale Child and Adolescent Sleep Clinic in Toronto has read these latest studies and was involved in research on Ontario high school students a few years ago that found that, with some exceptions, "the longer you sleep the better your grades."

"Sleep is not just a passive process, there are active things going on, you're metabolizing and putting out hormones and so on," Shapiro, a professor at the University of Toronto, said in an interview.

The Montreal study seems to fit with the growing literature that sleep is good for memory and good for brain growth, he said.

"They've shown that kids who have longer sleep have more cognitive skills, and so that probably means that one can infer that there's something about the sleep process that helps with cognitive development," he said.

"And so our attitude of making sleep expendable comes with a cost."

He called the cellphone study from Belgium "straightforward."

"One could have guessed that," he said of the after-bedtime phone calls and text messaging by teens. "They've documented it, but it's an important issue … you've got to recognize that sleep is a valuable part of life and you need to have a time that you're not disturbed in your sleep."

"Certainly having your cellphone as a potential disruptor because you have to be in touch with everyone all the time is a mistake. It's not going to lead to good function."

Chaya Kulkarni, a Toronto educator with the organization Invest in Kids, said the use of cellphones after lights out would be a concern for her as a parent.

"What's to stop a child from staying up until 2 in the morning, texting their friends, having nice long conversations …You have to have some rules in place," said Kulkarni, the mother of tweens aged nine and almost 12 who don't havecellphones.

Hard to get up earlier

As for back to school, Shapiro says it's relatively easy to allow one's sleep pattern to go later, but to move itearlier after a weekend or a summer vacation is not so easy.

"In some students they just power through it and they say 'OK I have to make that adaptation.' They become a little bit sleep-deprived and try and catch up with that sleep on the weekend."

However, some students can't do that and are late for school or, in extreme cases, don't get to school at all, he said.

"They're often accused of, for lack of a better expression, being bloody-minded — they want to just watch TV and be on their GameBoy and involved with e-mailing their friends and, as this one article suggests, phoning their friends late at night," he said.

"Although those are significant issues, for some of them it is simply biologically driven." He notedthat "teenage monkeys go to bed late and get up late."

Change routine

Kulkarni says that for younger kids, even if a family hasn't started the transition to earlier school bedtimes, it's not too late.

"I think what's important here is that you establish a routine for bedtime with the children that is going to be workable for everybody with the start of school," Kulkarni advised.

She also recommends a morning routine so that everyone can get out of the house on time.

"The adults in the family need to confer and need to say 'OK, what's every day going to look like, and who's doing what?"' she said.

"Sort out roles and responsibilities in terms of those morning and evening routines so that at the very least, on Tuesday or whenever the kids start, you're not sort of looking at each other going 'Oh, I thought you were doing that."'