Dynamic features of peer network experiences (membership fluidity and network interconnectedness) were examined for their role in African American and White early adolescents' sense of belonging in mathematics classrooms. Because these dynamic features are naturally present in adolescents' peer group affiliations, attention to them provides a more accurate representation of the peer experiences that adolescents actually encounter than research models that ignore these experiences. After controlling for fall classroom belonging, spring classroom belonging was greater for African American and seventh-grade students than for White and sixth-grade students. Multiple-group memberships promoted classroom belonging among African American and seventh-grade students but undermined belonging among White and sixth-grade students. Network stability did not differentiate belonging. Study limitations and implications regarding the nature of peer group experiences and the social bases of belonging are discussed. (Contains 2 figures, 1 footnote and 1 table.)