Preschool dosage, outcomes, and mechanisms: Why are two years better than one?

Abstract

Given recent expansions in preschool programs provided by school districts, there is a need to understand the association between preschool dosage (i.e., the number of years children attend preschool) and school readiness, and to identify factors that mediate these associations in order to maximize the efficacy of preschool for public school students. The current study examined the estimated effects of preschool dosage (one year vs. two years) on school readiness in the San Francisco Unified School District’s targeted preschool programs. Children who attended preschool for one year or two years were matched on race/ethnicity, sex, home language status, IEP status, subsidy status, and age (N = 2,368; Asian/PI=28%; Black=16%; White=14.0%; Latinx=30%; female=48 %; M_age=4.38). Path analyses tested two mediators: fall skills and attendance in the final year of preschool. Relative to one year, children with two years of preschool had higher cognitive, social-emotional, and literacy skills by the end of preschool. Fall skills and attendance during the final year of preschool mediated the estimated effects of preschool dosage on children’s skills at the end of preschool, with literacy being the most robust mediator among fall skills. Sensitivity analyses found these effects carried over to children’s total score on a school readiness screener administered at kindergarten entry.