The primary purpose of the present study was to examine the contributions of social, academic, and psychological characteristics of peer groups to individual development in the same and different domains in Chinese children. Participants included 1,864 elementary school students (945 boys, M[subscript age] = 11 years) in China. One-year longitudinal data on social competence, academic functioning, and psychological problems were obtained from peer nominations, teacher ratings, school records, and self-reports. Multilevel structural equation modeling analysis showed that group-level social competence, academic performance, and psychological problems had significant same-domain effects on later individual outcomes. Moreover, group-level social competence had a positive cross-domain effect on later individual academic performance and a negative cross-domain effect on later individual psychological problems. Group academic performance had a positive cross-domain effect on later individual social competence, and group psychological problems had a negative cross-domain effect on later individual social competence. The results suggest that affiliation with peer groups, particularly socially competent groups, may have pervasive implications for children's performance and adjustment from a developmental perspective.