Kevin Carey has a post with some data that was desperately in need of chartification so here we see the percentage of poor fourth graders in various cities who test as having achieved proficient (red) or basic (green) levels of competence according to NAEP scores. As you can see, though educating poor children is challenging everywhere, some of these cities are having much more success than are others. Obviously, there's more to "demographic factors" than whether or not you qualify for the school lunch program, but as far as quick arguments go it's pretty convincing evidence that there are things LA, Chicago, Cleveland, and DC could be doing to obtain the kind of better results that New York and Boston are getting with poor children.