The first results of a three-year longitudinal study of the social maps of children beginning the transition to adolescence are reported. This exploratory study is guided by Bronfenbrenner's conception of the ecology of human development, stressing the importance of a phenomenological orientation to development in the context of ecological transitions. The study focuses on characteristics of children's social networks (the web of relationships in which the individual is involved) as a function of neighborhood type, socioeconomic status, and level of physical maturation. The social heterogeneity of the social network (e.g., the relative salience of peers versus adults) is a primary concern. The child's and parent's perceptions of the network, of the people available to help the child, and the child's friends are compared within the context of ecological, socioeconomic, and maturational factors. The results (for one hundred eleven sixth-grade children from three contrasting neighborhood schools) shed some light on age