This study examined peer group processes in the classroom that can potentially explain how motivationally "rich" children get "richer" whereas motivationally "poor" children get "poorer." In contrast to research on group processes which focuses on socialization from group to individual, this study focuses on contributions from the individual to his/her group. The viewpoint taken for this study is that children actively choose group members based on their own self-system state, thereby creating their own peer environments in which they develop.Viewed as open complex systems, children's natural peer groups were examined using data collected from students and their teachers at five measurement points across a school year in four grade 4/5 classrooms. Out of 112 students, data were obtained for 94 (51 male, 43 female) children regarding their classroom engagement, peer network affiliations, and associative preferences ("ideal groups" of classmates with whom they would like to hang out). In an effort to overcome some of the challenges that group researchers face, methodologies argued to reliably capture children's networks and to measure the network's psychological characteristics were used. In addition, a hierarchical systems framework was applied whereby the underlying group processes could be examined across time. Two of seven hierarchical perspectives were used to examine influences from the individual to his/her network. Focusing first on the changing nature of a child's network, findings revealed a pattern of robust equilibrium. Networks showed an initial period of rapid change in member turnover (approximately 45%) during the first few months and then evolved quickly toward a stable (attractor) state of approximately 25% turnover the remainder of the year. Focusing next on the proximal processes by which the peer network emerges--selection and elimination--children were found to be more similar to those whom they would like to select than those whom they would like to eliminate. Taken together, the findings suggest that the child creates a peer context in the classroom that is stimulating and compatible to his/her own changes in engagement across the school year, thereby providing a possible explanation for how the motivationally "rich" get "richer" and the "poor" get "poorer".