The present study applied a developmental ecological perspective to the investigation of the relationship between preschool interactive peer play constructs and third-grade social adjustment and academic achievement. Participants in this investigation were drawn from a large, urban Head Start program in the Northeast to represent the program's geographic regions and overall demographic characteristics. A representative sample of 737 Head Start children, ranging in age from 3.0 to 6.1 years ([mean] = 4.4, SD = 0.6), were drawn from 30 classrooms for this study. From this representative sample, 373 children (47.5% male) were identified who entered the public school system and had complete data through third grade. In this investigation, two methods were utilized to investigate dimensions of the Penn Interactive Peer Play Scale (PIPPS). First, hierarchical setwise regressions were conducted to examine the unique contributions of interactive peer play dimensions to third-grade social adjustment and academic achievement. Second, typological analyses were used to identify distinct patterns of interactive peer play among Head Start children and to examine their differential relation to third-grade outcomes. Findings from hierarchical setwise regression analyses demonstrated the unique contributions of the preschool interactive peer play dimensions to third-grade social adjustment and academic achievement, above and beyond the variance attributable to child demographic covariates. Typological analyses produced six distinct types of preschool interactive peer play differentiated by high and low levels of the peer play dimensions. Resultant types related differentially to children's third-grade social adjustment and academic achievement. Overall, this study provided additional predictive validity to support the importance of interactive peer play as a critical preschool social competency related to later school success. Implications of these study findings for early childhood practice, policy, and future research are discussed. (author abstract)