A large portion of students do not get parental help with homework. Their parents aren't around, or don't actively participate in their lives. And that certainly means they won't pay for after school tutoring. Those are the kids most in need of systemic reform, not those who have parents that value education, where their only problem is just the schools themselves sucking. They will almost always succeed as long as their parents support them (and given enough income more likely than not move them into charter school or some other option).