Steven D. Levitt and Stephen J. Dubner, authors of Freakonomics, conclude that Head Start participation has no lasting effect on test scores in the early years of school, based on regression analysis of data from the Early Childhood Longitudinal Study. Levitt, one of the authors of Freakonomics, and Fryer come to the same conclusion in one 2004 paper they wrote.
Another issue has been that according to the most widely cited source supporting Head Start, children who finish the program and are placed into disadvantaged schools perform worse than their peers by second grade. Only by continuing to isolate these children (such as dispersing and sending them to better-performing school districts) can the gains be captured.