Greg J. Duncan

High-quality preschool programs are heralded as effective policy solutions to promote low-income children’s development and life-long wellbeing. Yet evaluations of recent preschool programs produce puzzling findings, including negative impacts, and divergent, weaker results than demonstration programs implemented in the 1960s and 70s. We provide potential explanations for why modern preschool programs have become less effective, focusing on changes in instructional practices and counterfactual conditions. We also address popular theories that likely do not explain weakening program effectiveness, such as lower preschool quality and low-quality subsequent environments. The field must take seriously the smaller positive, null, and negative impacts from modern programs and strive to understand why effects differ and how to improve program effectiveness through rigorous, longitudinal research.

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A survey targeting education researchers conducted in November, 2020 provides both short- and longer-term predictions of how much achievement gaps between low- and high-income students in U.S elementary schools will change as a result of COVID-related disruptions to schooling and family life. Relative to a pre-COVID achievement gap of 1.00 SD, respondents’ median forecasts for increases in achievement gaps in elementary school by spring, 2021 were very large – from 1.00 to 1.30 and 1.25 SD, respectively, for math and reading. Researchers forecast only small reductions in gaps between spring 2021 and 2022. Although forecasts were heterogeneous, almost all respondents predicted that gaps would grow during the pandemic and would not return to pre-pandemic levels in the following school year. We discuss some implications of these predictions for strategies to reduce learning gaps exacerbated by the pandemic as well as the mental models researchers appear to employ in making their predictions.

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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.

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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.

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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.

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