Language and literacy skills established during early childhood are critical for later school success. Parental engagement with children has been linked to a number of adaptive characteristics in preschoolers including language and literacy development, and family-school collaboration is an important contributor to school readiness. This study reports the results of a randomized trial of a parent engagement intervention designed to facilitate school readiness among disadvantaged preschool children, with a particular focus on language and literacy development. Participants included 217 children, 211 parents, and 29 Head Start teachers in 21 schools. Statistically significant differences in favor of the treatment group were observed between treatment and control participants in the rate of change over 2 academic years on teacher reports of children's language use (d = 1.11), reading (d = 1.25), and writing skills (d = 0.93). Significant intervention effects on children's direct measures of expressive language were identified for a subgroup of cases where there were concerns about a child's development upon entry into preschool. Additionally, other child and family moderators revealed specific variables that influenced the treatment's effects. (Contains 1 figure and 4 tables.)