@snarltron, I think you would have to read the original papers to draw any conclusions. For elementary school students, “the average correlation between time spent on homework and achievement … hovered around zero,” or no relationship. This may be because younger students have less-developed study habits and are less able to tune out distractions at home, Cooper says. I would say, this may be because the better students complete the homework faster and then go into school and perform better while having spent less time doing homework.
Kids have to practice reading to do well in school. And they have to learn their math facts to do well in school. It’s crippling at higher grade levels if they don’t read fluently and if they don’t know basic arithmetic. Either this can happen as homework, or it can happen in school, taking away instructional time for routine practice/drill. I would like to hope that more goes on in a good classroom than just drilling math facts or reading silently. If a teacher can’t assign useful homework, I would question whether much of value is going on in the classroom either.