The United States is witnessing two major trends in its rising cohorts of young children preparing to start school: an increase in the utilization of formal (e.g., center-based) childcare options in the year before starting kindergarten and an increase in the share of these young children who come from immigrant families. Given that many children from immigrant families start school at a disadvantage relative to native-born children, researchers, policy makers, and practitioners have inquired into which prekindergarten alternatives might be most effective at boosting school readiness for this group of children. This review covers the effects of formal versus informal prekindergarten alternatives in the year before entering school on both academic and socioemotional measures of school readiness for children in immigrant families. In general, the results of this literature review show positive effects of formal prekindergarten in the year before kindergarten for children in immigrant families. This is evidenced across both academic and socioemotional domains of readiness measures. That said, there are several, noteworthy common limitations in this body of literature, which can be used to shape future research agendas and policy dialogue. (author abstract)