By W. Bradford Wilcox, a sociology professor at the University of Virginia who directs the Home Economics Project of the American Enterprise Institute and the Institute for Family Studies.Forget the gender gap. The fundamental divide in the United States today runs along the lines of class and marriage. College-educated Americans and their children reap the benefits of comparatively stable, happy marriages, while less-educated Americans—especially the poor and the working-class—are more likely to struggle with family lives marked by discord and marital instability. This two-tiered ...