No, its actually not the lack of resources. Kids who get bussed to better schools as part of the exchange program are still very likely to fail.
And no matter how you spin it, a lot of the blame does fall on the kids themselves. Even when bussed, they still tend to hang with the wrong crowd, are more likely to do drugs/get in trouble, etc.
You can't try to blame everything except the kid themselves, they, along with everything else are part of the issue.
Intelligence and behaviour can partly be taught but there is a large part that is genetic as well. Even if you equalized everything right now, within a few decades, society would quickly stratify itself again because of the differences in individual humans -- differences that in large part are genetic. Its been proven with other mammals and I expect humans to be no different. Once again, this does not apply to any race as a while, but only to individual humans and genetic lines.
If your parents were smart and good at math then your chances of being smart and good at math are going to be higher than average. I know people will come up with some anecdotal evidence, but those do not thwart scientific probability. All humans are simply not created equal in terms of talent and those talents tend to be passed down genetic lines. With humans, the decent probability of marrying up or down the social ladder dilutes this as a whole so the effect may not be profound as in other species where the weak or un-adapted simply die out.
I would guess that large research has not been done in humans regarding this because even if the results support what I think in this post, they wouldn't be able to report in a science journal without creating a firestorm, thats just how stupidly politically correct we are nowdays.
I actually don't think the gap in performance has that much to do with the genetics of intelligence, but has a lot more to do with personality and attitude in class/more likely to be disruptive or not listen. Traits like these in other mammals have also been strongly linked to genetics.