The widening wage gap between college and high school graduates is down to the growing difference in their ability and test scores

The past century has seen a massive expansion of education in the U.S, with the vast majority now graduating from high school and more than a quarter from college. At the same time, the wage gap between college and high school graduates has grown from 35 to 50 percent. By looking at the results of standardized test scores from two dozen 20th century studies, Todd Schoellman and Lutz Hendricks find that the expansion of education has led to a decline in mean test scores of high school graduates but not college graduates. The change in mean test scores explains why wages for high school workers have grown more slowly than the wages for college workers, and thus why the wage gap between the two groups has grown.