We are grateful to Paul Barton, Stephen Hamilton, Jerry Hayward, James Rosenbaum, Laurence Steinberg, two anonymous reviewers, and especially David Boesel for helpful comments on early drafts. Work on this report was supported by the U.S. Department of Education through the Office of Vocational and Adult Education, the National Center on the Educational Quality of the Workforce, the National Assessment of Vocational Education, and the National Research Council of the National Academy of Science. However, the conclusions and opinions stated here are the authors' alone and do not necessarily reflect the views or positions of the U.S. Department of Education or the National Academy of Science.