Program Evaluation and Research Designs
---- Acknowledgements -----
We are grateful to Diane Alexander and Pauline Leung, who provided outstanding research assistance. We thank Orley Ashenfelter, David Card, Damon Clark, Nicole Fortin, Thomas Lemieux, Enrico Moretti, Phil Oreopolous, Zhuan Pei, Chris Taber, Petra Todd, John Van Reenen, and Ken Wolpin for helpful suggestions, comments, and discussions. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research.