Abstract Applying sociological and developmental theoretical perspectives to educational policy issues, this study analyzed data from 7,710 children from low-income families in the Early Childhood Longitudinal Study-Kindergarten Cohort. The goal was to examine how much the association between phonics instruction in kindergarten classrooms and childrenâ€™s reading achievement during the first year of school in the low-income population would depend on whether children had previously attended preschool as well as the socioeconomic composition of their elementary schools. Lagged linear models with a series of sensitivity tests revealed that this association was strongest among children from low-income families who had not attended preschool and then enrolled in socioeconomically disadvantaged elementary schools and among children from low-income families who had attended preschool and then enrolled in socioeconomically advantaged elementary schools. These findings demonstrate how insights into educational inequality can be gained by situating developing children within their proximate ecologies and institutional settings, especially looking to the match between children and their contexts. They are especially relevant to timely policy discussions of early childhood education programs, classroom instructional practices, and school desegregation.