How Much Is Too Much?

Young children, at least among those from poor families and within the domains of cognitive growth and school readiness, benefit from exposure to preschool or childcare centers. Carefully controlled experiments, exemplified by the Perry Preschool or the Abecedarian Project, have long shown sustained effects on cognitive growth for children from poor Black families. Even beyond these so-called “boutique programs,” larger public initiatives, such as the Chicago Child-Parent Centers, show encouraging results, as do center programs of naturally varying quality spread across different states.

What is not known is whether the effects of preschool centers vary by intensity of exposure and for children from different backgrounds. Little is known, for instance, about whether middle-class children experience the same bump in early learning, comparable with the gains displayed by poor children, when they attend a center program

In this report, our analysis extends recent work by Magnuson, Ruhm, & Waldfogel (2004) to consider the effects of different preschool or childcare arrangements on children’s cognitive and social proficiencies at the start of kindergarten, focusing on how the duration and intensity of participation affect children across developmental domains. The analysis also focuses on how such benefits or decrements in development may vary across children from different social classes and ethnic groups. These issues are directly germane to debates over whether extending free preschool to all children is a cost-effective policy strategy, whether full- or half-day programs are advisable, and which groups of children would likely benefit at what level of magnitude.

The analysis, drawing on data from the Early Childhood Longitudinal Study (ELCS), starts by asking the question: Does exposure to a preschool center in the year(s) before kindergarten advance children’s cognitive and social development? It then asks how the relationships between center exposure and child development may vary for diverse groups of youngsters who come from different income and ethnic groups.

Finally, our analysis focuses on the effects of the intensity and duration of center attendance—as measured in years, months per year, and hours per week—on child outcomes. Never before has the field been able to test these relationships with a large, nationally representative sample of young children with such rich background data on their families and a priori parental practices.