Yes, ideally the parents should be the ultimate motivators and disciplinarians of their children. And poor parents do have a greater incentive to take this role seriously, stressing the value of education to their children and being active in their academic lives, so that they can also have a better life when their child becomes a successful and wealthy doctor/engineer etc. This attitude is prevalent among many immigrant families I know, and it is admirable -- they enter the U.S poor and become comfortably upper-middle class in 20-30 years simply by drilling the value of education into their children and refusing to accept less than excellent grades on their report cards.
But this culture, of utmost appreciation for education, doesn't exist among African American families. Most black children are now raised by single mothers who are often too busy trying to make ends meet for themselves and their children to pay attention to how their children are getting along in school. Even in two parent households, it is often the case that one parent has to work two jobs to meet the needs of the family and has no time to monitor their children. For this reason, so many black children don't get the support they need at home in order to succeed in school and are more likely to be influenced by negative peer pressure. This is where schools should step in. Instead of condemning black parents for being absent from their children's educational development, we would better off looking at where schools can fill that void. One program, KIPP, has made strides in this regard. With longer school days and significant teacher involvement in student's lives, they've increased test scores and college attendance rates in some low-income communities. Expanding this sort of service to more at-risk students would present some major challenges, especially in the current public education environment. But we can at least learn a thing or two from programs like KIPP and work through those some of those challenges, thus creating a more positive, productive culture among future black adults instead of vilifying their parents for their shortcomings.