(FORTUNE Magazine) – There is a growing income disparity in the work force between those with and without a college degree. How can high schools better prepare students headed straight for the job market? New research examines what gives non-college- bound high schoolers future earning power -- and what doesn't. Using an enormous database collected by the Department of Education, economists at the University of Pennsylvania calculated an array of correlations between future income and various features of high school life. The most important factors have to do with real-world experience. High schools that provide job listings for their students tend to produce workers who earn about $1,400 more per year than those who came from schools that did not give such information. Students enrolled in vocational programs, like metal shop, make roughly $1,400 less than those who concentrated on basic academics. Most striking of all, students who had part-time jobs earn more than those who didn't, but the amount of homework assigned made no difference. Says David Crawford, an author of the study, only half-jokingly: "Tell your kid to stop doing his homework and get a job at McDonald's."--J.A.