With DD7, if I see that he's spending more time than he needs to on his work, I give him a time limit, e.g., 10 more minutes to finish the page of math problems. Whatever is left will be homework, i.e., we will move on with the school day and he can finish the math problems after school (and before he gets to play video games). I started this over a week ago and, guess what: he hasn't had homework once yet. :D