The writers seem somewhat puzzled about what's happening.
Education appears to play a significant role and so do race and "the tendency of well-off parents to have healthier children or children more likely to get treated for health prolems."
Apparently they haven't made the connection as to how the GOP's fixation on tax cuts for the WSJ-reading-class might have affected the ability of working families to educate and get health care for their kids. Not to mention the elimination of affirmative action, since they're sure that was an insult to blacks.
Equality of opportunity for all children to a college or post-high-school vocational education as well as healthcare sounds like a platform for someone to run on.