Currently, our national education policy expects something we cannot possibly achieve if schools alone are seen as responsible for student achievement. Our national goal is that all social-class differences in education outcomes will disappear by the year 2014. However, when 2014 arrives and gaps have not disappeared, we will judge that schools have failed. Policies will follow from that judgment. But most of these policies will not work, because we will have made an incorrect diagnosis of the problem and therefore formulated an incorrect or incomplete treatment as a solution.Still, it looks like achievement gaps (at least race-based ones) are steadily closing, according to the newest NAEP data released just today. Political analysis from Eduwonk here.
P.S., why doesn't NAEP disaggregate data by class? I guess it's because they rely on data that students report themselves. Parents' highest level of education is probably as close as they can get, and if you look at those trendlines the gaps between "less than high school" and "graduated from college" really have not closed at all since 1978.