In this study we examine the extent to which preschool education can reduce social background differentials in learning outcomes across countries; our focus is on whether the benefits of preschool attendance for children depend on other family inputs such as parents’ education and their pedagogical involvement during early childhood. We use the 2011 Progress in International Reading Literacy Study, which provides a standardized measure of reading literacy among students in 4th grade. Our sample contains data on 119,008 individuals from 28 developed countries. The presented evidence confirms that preschool is visibly beneficial in most cases, but also that benefits are lower for children who have more involved or more educated parents. Rather than complements to, parental involvement and parental education seem to be substitutes for preschool attendance in children’s skill production function. As such, preschool education reduces social inequalities in educational achievement. Yet, its equalizing potential could have been overstated in previous debates.