4 models (risk, protective, potentiator, and person-environment fit) comparing the associations among ethnicity, income, and structural characteristics of families and neighborhoods on childhood aggression and peer relations were explored. The 1,271 second- through fifth-grade (M= 9.9 years) children were assigned to 1 of 8 family types based on ethnicity, income, and household composition, and their addresses were used to define low- or middle-SES neighborhoods using neighborhood census data. Middle-SES neighborhoods operated as a protective factor for reducing aggression among children from high-risk families, interacted with family type to produce poor person-environment fit resulting in a greater likelihood of being rejected by one's peers, and potentiated the development of home play companions for children from low-risk families. Developmental and gender differences were also explored. Results are discussed in terms of the need for broader contextual factors to be considered in studying children's social and behavioral development.