NPR has a roundup of recent research on homework. One near-consensus seems to be that about 10 minutes per grade level is kind of sweet spot. This is the U.S. system we’re talking about, which goes up to 12 grades so therefore two hours. I did a lot more homework than this in high school.

Let’s start with something called the spacing effect. Say a child has to do a vocabulary worksheet. The next week, it’s a new worksheet with different words and so on. Well, research shows that the brain is better at remembering when we repeat with consistency, not when we study in long, isolated chunks of time. Do a little bit of vocabulary each night, repeating the same words night after night.

Similarly, a professor of psychology at Washington University in St. Louis, Henry “Roddy” Roediger III, recommends that teachers give students lots and lots of little quizzes, which he says strengthen the brain’s ability to remember. Don’t fret. They can be low-stakes or no-stakes, says Roediger, it’s the steady recall and repetition that matter. He also recommends, as homework, that students try testing themselves instead of simply re-reading the text or class notes.

There’s also something known as interleaving… there’s evidence that students learn more when homework requires them to choose among multiple strategies — new and old — when solving problems. In other words, kids learn when they have to draw not just from what they learned in class that day but that week, that month, that year.

One last note: Experts agree that homework should generally be about reinforcing what students learned in class (this is especially true in math). Sometimes it can — and should — be used to introduce new material, but here’s where so many horror stories begin.