In this article, inclusion and exclusion are interpreted not as functions of individual developmental deficit but rather as socially constructed phenomena within the peer group, highlighting the need for teachers to intervene with the entire class rather than focusing on perceived social skills deficits of particular children. The three sections in this document describe how children in this study used play materials and themes to create play group affiliations, restrict or challenge group membership, and stretch peer social boundaries. The final section offers classroom implications and suggestions for teachers to help young children form more inclusive play groups.