The solution to primary school homework is simple -- don't just pile up tasks for them to complete. Instead they should be taught how they can effectively study for themselves and not have to slave over unrelated homework. Then, by the time they reach high school, they would have figured out that what the teacher gives them isn't important - it's what they actually learn that is related to the course.
Kids come home from school, often packed with homework to complete by the deadline. Not all, but definitely a considerable amount of children anyway. They do not need to be given a large amount of work to complete at home, especially those in the low grades. It would be a better idea to influence them to study the material themselves rather than given a preset homework sheet designed for everyone.
School's seem to overlook a lot. Students would spend a lot less time doing homework if they weren't given much, but knew that they had to study it for themselves. They would also learn the same amount in the process making homework much more efficient and effective. It would carry on through high school. Students, particularly smarter ones, won't have to be told what to do for homework. They will just know "learn this" but not to be bothered by busywork.