They're not learning because teachers aren't teaching. And this isn't their fault! Rather than teaching, they spend most of their time trying to control the behavior of children who don't have the self-control necessary to be receptive to learning. Can anyone be expected to be both a classroom teacher and a behavioral therapist? Any parent who doubts this should visit a classroom and see the obstacles these teachers face.
School administrators at the district and state levels should get out of their offices and spend a day as a substitute teacher. Perhaps then they'll comprehend the problem and divert some of their resources to supporting these teachers in creating an environment where their students can actually learn.