The studying that middle school and high school students do after the dismissal bell rings is either an unreasonable burden or a crucial activity that needs beefing up. Which is it? Do American students have too much homework or too little? Neither, I’d say. We ought to be asking a different question altogether. What should matter to parents and educators is this: How effectively do children’s after-school assignments advance learning?

The quantity of students’ homework is a lot less important than its quality. And evidence suggests that as of now, homework isn’t making the grade. Although surveys show that the amount of time our children spend on homework has risen over the last three decades, American students are mired in the middle of international academic rankings: 17th in reading, 23rd in science and 31st in math, according to results from the Program for International Student Assessment released last December.

“Spaced repetition” is one example of the kind of evidence-based techniques that researchers have found have a positive impact on learning. Here’s how it works: instead of concentrating the study of information in single blocks, as many homework assignments currently do — reading about, say, the Civil War one evening and Reconstruction the next — learners encounter the same material in briefer sessions spread over a longer period of time. With this approach, students are re-exposed to information about the Civil War and Reconstruction throughout the semester.