There’s a huge debate about homework and whether it helps kids learn during the school year. But everyone agrees that homework can take lots of time. The most commonly accepted guidelines recommend one hour for middle school and two hours for high school. However, I think this amount of time on homework every day can be too much.

The nightly hour many middle schoolers spend on homework adds up to about 180 hours over a school year. That’s time that kids could be playing sports, reading books or just taking a break after a long day.

It’s common for high school students to devote twice as much time, about two hours daily, to their homework. And some schools require much more homework. In some school systems, even kindergartners do some homework.

Does making kids study in what could be their personal time pay off? Homework appears to work best when the teacher and students are clear about what it’s for and the assignments are worthwhile. While I do believe doing some homework is helpful, I don’t think it should be assigned unless it’s necessary.

My research group and I found this out by examining survey responses of students. They told us how much time they spent doing homework, what grades they got and how they did on standardized tests.

The evidence we found suggests that students who spend more time doing homework don’t necessarily get better grades. But it may help them get higher scores on the standardized tests that nearly all American public school students take. That is because doing more homework to practice things you know can help you get better and faster at doing those things.

From what I’ve seen with my own students, those who seem to spend a lot of time on homework are usually struggling to understand what they are being asked to do. That could explain why devoting more time to homework doesn’t automatically improve grades.

In these situations, I believe students would probably be better off learning the material in class with their teacher before going home and trying it on their own. One benefit is what happens when students get back this extra time after school: There’s more time for sports, music, books and friends.

Everyone needs a break after a long day of work, after all. And that includes students.

Author Bio: Robert H. Tai is an Associate Professor of Education, University of Virginia