This is partly a difference between high and low-SES school communities. In very low SES urban neighborhoods, especially with many families that do not speak English, the expectation that parents will help with work at home to any significant degree simply won't wash.
My district does not permit using homework for school grades -- all work used to evaluate student learning must be done in school. The expectation is that all the teaching required will also be done in school. Our primary division is really quite strong on the teaching side of things, with the vast majority of kids meeting or exceeding expectations for their grade and a lot of support and good instructional practices (if not curricula) are in place.
Unfortunately, with high mobility and transience, by the middle school years there is a huge influx of students lacking the preparation "our" kids received and the achievement is much more varied and the task confronting classroom teachers almost impossible.
Nevertheless, a lot of learning does take place at school, and despite the odds, a number of our students are successful in getting into competitive secondary schools (usually these are students we have had from the beginning).
We have a long way to go, but the focus is certainly on teaching the kids *in school* and not on relying on parents or tutors to do it -- that is just not going to happen.