from here
1. The negative effects of homework are well known. They include children’s frustration and exhaustion, lack of time for other activities, and possible loss of interest in learning. Many parents lament the impact of homework on their relationship with their children; they may also resent having to play the role of enforcer and worry that they will be criticized either for not being involved enough with the homework or for becoming too involved.
2. The positive effects of homework are largely mythical. In preparation for a book on the topic, I’ve spent a lot of time sifting through the research. The results are nothing short of stunning. For starters, there is absolutely no evidence of any academic benefit from assigning homework in elementary or middle school. For younger students, in fact, there isn’t even a correlation between whether children do homework (or how much they do) and any meaningful measure of achievement. At the high school level, the correlation is weak and tends to disappear when more sophisticated statistical measures are applied. Meanwhile, no study has ever substantiated the belief that homework builds character or teaches good study habits.
3. More homework is being piled on children despite the absence of its value. Over the last quarter-century the burden has increased most for the youngest children, for whom the evidence of positive effects isn’t just dubious; it’s nonexistent.
It’s not as though most teachers decide now and then that a certain lesson really ought to continue after school is over because meaningful learning is so likely to result from such an assignment that it warrants the intrusion on family time. Homework in most schools isn’t limited to those occasions when it seems appropriate and important. Rather, the point of departure seems to be: “We’ve decided ahead of time that children will have to do something every night (or several times a week). Later on we’ll figure out what to make them do.”
more info on what Teachers and schools should do (by same person)
