Greg Duncan

This paper uses meta-analytic techniques to estimate the separate effects of the starting age, program duration, and persistence of impacts of early childhood education programs on children’s cognitive and achievement outcomes. It concentrates on studies published before the wide scale penetration of state-pre-K programs. Specifically, data are drawn from 67 high-quality evaluation studies conducted between 1960 and 2007, which provide 993 effect sizes for analyses. When weighted for differential precision, effect sizes averaged .26 sd at the end of these programs. We find larger effect sizes for programs starting in infancy/toddlerhood than in the preschool years and, surprisingly, smaller average effect sizes at the end of longer as opposed to shorter programs. Our findings suggest that, on average, impacts decline geometrically following program completion, losing nearly half of their size within one year after the end of treatment. Taken together, these findings reflect a moderate level of effectiveness across a wide range of center-based programs and underscore the need for innovative intervention strategies to produce larger and more persistent impacts.

More →

Using an additional decade of CNLSY data, this study replicated and extended Deming’s (2009) evaluation of Head Start’s life-cycle skill formation impacts in three ways. Extending the measurement interval for Deming’s adulthood outcomes, we found no statistically significant impacts on earnings and mixed evidence of impacts on other adult outcomes. Applying Deming’s sibling comparison framework to more recent birth cohorts born to CNLSY mothers revealed mostly negative Head Start impacts. Combining all cohorts shows generally null impacts on school-age and early adulthood outcomes.

More →

We present a reanalysis of the Tennessee Voluntary Prekindergarten Program (TNVPK), a state-funded program designed to promote the school readiness of 4-year-olds from low-income families. Oversubscribed programs used a lottery to randomly assign prospective enrollees a chance to attend TNVPK. We found that assignment to the program had largely null effects on measures of behavior, attendance, and retention collected during elementary school. TNVPK increased enrollment in special education by 4% between kindergarten and grade 3, and generated negative but generally statistically insignificant impacts on third-grade state test scores. We explore reasons for fadeout as well as threats to internal validity.

More →