School kids who get to bed early rather than staring at their devices at night may be better equipped to control their behavior, a new study suggests.

Researchers found that 8- to 11-year-olds who got adequate sleep and had limits on "screen time" were less likely than their peers to report problems with impulsive behavior.

Impulsivity is generally described as a tendency to act without thinking, or an inability to wait for something you want. It's a central problem in attention-deficit/hyperactivity disorder (ADHD). Later in life, impulsivity may also make kids vulnerable to other problems, like substance abuse and other forms of addiction, said lead researcher Michelle Guerrero.

Guerrero said her team wanted to see what factors might affect that tendency to "act before thinking." In general, the researchers found, kids were less likely to report impulsive behavior if they met recommendations for sleep and screen time. That meant 9 to 11 hours of sleep each night and no more than 2 hours a day devoted to "recreational" screen time. (School work didn't count.)

However, the findings only point to a correlation, said Guerrero, a fellow with the Children's Hospital of Eastern Ontario Research Institute, in Ottawa, Canada. They do not prove earlier bed times and screen limits will actually prevent impulsivity, she explained. "Is it that impulsive kids don't meet the recommendations, or that kids who don't meet the recommendations become more impulsive?" Guerrero said.

The most likely scenario, she added, is that the relationship goes both ways—creating something of a vicious cycle. That point was echoed by Richard Gallagher, an associate professor of child psychiatry at NYU Langone Health, in New York, NY. According to Gallagher, who was not involved in the study, it's known that kids with ADHD tend to sleep less than their peers, for example. And it's easy to see how impulsive kids would be more prone to staying up late and playing video games or obsessively checking phones.

At the same time, Gallagher said, insufficient sleep can certainly affect kids during the day—dulling their ability to concentrate and just generally making them "cranky." "That could look a lot like impulsivity," Gallagher noted.

Why would screen time matter? Guerrero's team points to one theory: Too much time on devices—which often demand immediate responses, whether on social media or in video games—may affect kids' ability to self-regulate.

But the other issue, Guerrero said, may be what kids are not doing during those hours in front of a screen—like sleeping. "These things are very interrelated," she said.

The findings, published online August 14 in Pediatrics, are based on over 4,500 Canadian kids aged 8 to 11. The researchers looked at whether the children met Canadian recommendations for sleep, screen time, and physical activity (60 minutes of moderate to vigorous exercise each day).

The kids completed a few standard questionnaires on impulsivity—asking them the extent to which they agreed with statements like, "When I am upset, I often act without thinking," and "I finish what I start."

In general, kids who fell short on sleep and spent too much time on screens had higher impulsivity scores. Exercise, on the other hand, did not show much of a connection. While none of that proves cause and effect, both Guerrero and Gallagher said that parents can take away some practical messages. Guerrero suggested setting a time in the evening when devices have to be turned off—which should help kids get to sleep.

It's also important to see the wider context, Gallagher said: Is screen time replacing not only sleep, but exercise, homework, or face-to-face time with friends and family? Guerrero agreed that the bigger picture—including not only the amount, but the content of kids' screen time—clearly matters.

And then there are parents' habits. Guerrero acknowledged that parents may have to be on their devices at times, for work reasons. But it's important to set limits for yourself, too. "It's hard to tell your kids, 'Get off your device,' if you're always on yours," Guerrero said.