Most parents don’t need a scientist to tell us that if our kids (and we) don’t get enough sleep, life can sometimes get ugly. But if having a little research to back us up can be reassuring, a new study published in the Journal of Pediatrics will help.

The study found that kids who slept less than 7 hours per night were more sleepy the next day (doh!), did worse on tests in school, and had more behavior problems. A different study also found a connection between lack of sleep and obesity, which makes getting enough sleep as important to children’s wellbeing as eating right and exercising.

In the study, Reut Gruber and his associates used two groups of kids: those who slept less than 7 hours per night and those who got 7-11 hours of shuteye. Teachers—who didn’t know which kids were in which group—were then asked to assess their students’ mood and behavior. They found exactly what you’d expect: the tired kids were moodier and have more behavior problems than those who’d had enough sleep.

What’s especially noteworthy is that all it took was as little as 15 minutes of extra sleep to greatly improve kids’ mood and behavior. Sleep “is associated with difficulty in the modulation of impulse and emotion,” writes Gruber. Therefore, “sleep must be prioritized, and sleep problems must be eliminated” if kids are to have the best chance of succeeding in school and in life.