https://astralcodexten.substack.com/p/nobody-knows-how-well-homework-works

Yesterday I wrote about bottlenecks to learning. I wanted to discuss the effectiveness of homework. If it works well, that would suggest students are bottlenecked on examples and repetition. If it works poorly, it would have to be something else.

Unfortunately, all the research on this (showcased in eg Cooper 2006) is terrible.

Most studies cited by both sides use "time spent doing homework" as the independent variable, then correlate it with test scores or grades. If students who do more time on homework get better test scores, they conclude homework works; otherwise, that it doesn't.