http://www.businessinsider.com/we-now-know-more-about-how-ne...
I would argue that the reason suburban students are better are most likely because their parents are also better, whatever being a 'better' parent means in this case.
Poorer communities often have a culture so different than the average HN reader that most of us can't possibly understand it. (I learned this as a result of being a foster parent)
If you were trying to rank parents wouldn't "prioritizes their children's education" be a factor in determining which parent was better? Just because something is a cultural difference doesn't mean we can't say it is better or worse.
As nice and easy it would be to measure a person's worth as a parent by how well their kids do in school, or how much they make as an adult (like this article), I don't think that's reasonable at all.