Steven Barnett and Clive Belfield examine the effects of preschool education on social mobility in the United States. They note that under current policy three- and four-year-old children from economically and educationally disadvantaged families have higher preschool attendance rates than other children. But current programs fail to enroll even half of poor three- and four-year-olds. Hispanics and children of mothers who drop out of school also participate at relatively low rates. The programs also do little to improve learning and development. The most effective programs, they explain, are intensive interventions such as the model Abecedarian and Perry Preschool programs, which feature highly qualified teachers and small group sizes. State preschool programs with the highest standards rank next, followed by Head Start and the average state program, which produce effects ranging from one-tenth to one-quarter of those of the best programs. Typical child care and family support programs rank last. Barnett and Belfield point out that preschool programs raise academic skills on average, but do not appear to have notably different effects for different groups of children, and so do not strongly enhance social mobility. In such areas as crime, welfare, and teen parenting, however, preschool seems more able to break links between parental behaviors and child outcomes. Increased investment in preschool, conclude Barnett and Belfield, could raise social mobility. Program expansions targeted to disadvantaged children would help them move up the ladder, as would a more universal set of policies from which disadvantaged children gained disproportionately. Increasing the educational effectiveness of early childhood programs would provide for greater gains in social mobility than increasing participation rates alone. The authors observe that if future expansions of preschool programs end up serving all children, not just the poorest, society as a whole would gain. Benefits would exceed costs and there would be more economic growth, but relative gains for disadvantaged children would be smaller than absolute gains because there would be some (smaller) benefits to other children.