Impacts and Mechanisms of Preschool Dosage: Why Are Two Years Better Than One?

• In Event: Early Childhood Research: Lessons From a Research-Practice Partnership

Abstract

Previous research indicates that children who begin Head Start-type preschool programs at age three and receive two years of preschool demonstrate stronger literacy, math, cognitive readiness, and social-emotional skills in kindergarten relative to children who begin preschool at age four and attend for only one year (Domitrovich et al., 2013; Reynolds, 1995; Wen et al., 2012). Less is known about the role of preschool dosage in the context of more recently expanded state and local school district programs (Friedman-Krauss et al., 2020), and about the mechanisms that facilitate the effects of preschool dosage on later outcomes. By investigating these mechanisms within a local school district, we can identify and target malleable factors that contribute to skill levels by the end of preschool and at kindergarten entry (Fairchild & MacKinnon, 2014). Our RPP uniquely positioned us to address these mechanistic questions by providing access to data on students’ cognitive, social-emotional, and early literacy skills over time, and valuable insights into the minutiae of the district’s preschool program.

This study examined how preschool dosage (one year vs. two years) affects kindergarten-entry skill levels in a San Francisco Bay Area school district. Children who attended preschool for one year or two years were matched on race or ethnicity, sex, home language status, and age (N = 2,504; Asian/PI = 30.8%; Black = 14.7% ; White = 13.3%; Latinx = 28.5%; female = 48.6%; Mage = 4.39). By the end of age-4 preschool, experiencing two years of preschool had a positive effect on children’s cognitive skills (β = 0.145, SE = 0.026, p < .001), social-emotional skills (β = 0.157, SE = 0.025, p < .001), and early literacy skills (β = 0.171, SE = 0.025, p < .001) relative to experiencing only one year. By kindergarten entry, two years of preschool had a positive effect on children’s literacy skills (β = 0.093, SE = 0.026, p < .001) relative to only one year of preschool, but no longer had a significant effect on their cognitive (β = 0.037, SE = 0.025, p = .128) or social-emotional skills (β = 0.034, SE = 0.024, p < .165).

We found that cognitive, social-emotional, and early literacy skills at age-4 preschool entry significantly mediated the effect of dosage on cognitive, social-emotional, and early literacy skills by the end of preschool and in kindergarten. Age-4 attendance mediated the effects of preschool dosage on cognitive, social-emotional, and early literacy skills at the end of preschool, and on cognitive and literacy skills in kindergarten. There was no significant indirect effect of dosage or age-4 attendance on social-emotional skills in kindergarten.

Our results suggest that preschool attendance is both an important and malleable mechanism in improving child outcomes. These findings should encourage teachers and school leaders to develop classroom- and community-driven strategies to improve attendance for families in their first year of preschool to ensure that all students, especially those facing significant barriers to attendance, can experience the maximum benefits of preschool.

Authors

• Meghan McDoniel, Stanford University

• Catie Connolly, Stanford University

• Lily Steyer, Stanford University

• Jelena Obradovic, Stanford University