On the flip side, cutting back on kids' time asleep seems to make them more likely to cry, lose their temper and become frustrated, according to the researchers, who published their findings in the journal Pediatrics on Monday.

"You can think about it from a lot of different angles. What we are showing here is that it can go both ways in terms of behavior and academic performance," said Reut Gruber, of Montreal's McGill University and Douglas Research Center, who led the study.

While Gruber's team is not the first to link sleep and behavior, few studies have looked at whether more sleep actually leads to better behavior in school children.

For the study, they recruited 33 children between seven and 11 years old to be followed over two weeks.

For the first week, the researchers monitored how long the kids slept - about 9.3 hours, which is short of the 10 hours suggested by the U.S. National Institutes of Health.

The children were then split into two groups for the second week.

One group's parents were told to add an hour to their kids' usual time asleep, while the other group was told to cut their kids' sleep by an hour.

Half of the children did lose an hour of sleep each night, but the other group was only able to add about 30 minutes.

Still, that half hour seemed long enough for teachers to notice an improvement in the kids' behavior.

After the first week of monitoring, the teachers answered questions that rated the children's emotions, moodiness and restlessness at school on a scale from zero to 100, with higher scores indicating worse behavior and scores above 60 signaling a behavioral problem.

The baseline score for both groups of kids before the sleep manipulation began was about 50.

After a week of the experimental sleep changes, teachers - who did not know which group any of the children were in - rated the kids again.

The children who got that extra 30 minutes of sleep during the second week scored, on average, about 47, meaning their behavior had improved.

Meanwhile, teachers rated the kids who lost an hour of sleep each night at about 54, indicating their behavior had gotten worse.

Neither of those changes signals an extreme difference in the children's behaviors, said Gruber. But, she added, it would be enough of a difference to make the teachers notice.

Unsurprisingly, the parents of those who got an extra 30 minutes of sleep also said their children weren't as tired throughout the day, while the opposite was true for parents in the other group.

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"The thing that was surprising was how little sleep extension could affect functioning on a day-to-day basis," said Dr. Umakanth Khatwa, sleep lab director at Boston Children's Hospital in Massachusetts, who was not involved with the new study.

Gruber told Reuters Health that while the study only included 33 kids, it was still able to show more sleep leads to better behavior.

However, the researchers do write that not all of the study's participants were blinded as to which children lost or gained an hour of sleep, because the parents had to be in the know. That may have influenced the parents' reporting of sleepiness throughout the day, they say.

Gruber said that it can be hard for parents to add time to their kids' sleep schedule, but she said one of the keys is to eliminate interferences, such as late-night sports practice.

Khatwa agreed. "A lot of practices are going into evening now… And by the time you're done, your body is riled up and you need time to wind down," he said.

Gruber said one way to add the extra sleep could be to add 15 extra minutes of sleep at night and in the morning.

"Once it becomes a routine, the children won't really care about it," she said.

But Khatwa said it's also important for parents to know their children's specific sleep needs.

"I don't want parents to take this and force their kids to sleep longer… Parents need to have realistic expectations," he added. "You need to let them sleep long enough so they can function normally."

Gruber said that it's important for schools to educate children that getting enough sleep is just as important as eating right and getting enough exercise.

SOURCE: bit.ly/RwOI3p Pediatrics, online October 15, 2012.

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