- Ethnic group differences in the contributions of self-definition (self-worth and efficacy) and interpersonal relatedness with parents and peers to changes in psychological and school adjustment were examined among 448 White, Black, and Latino girls and boys (11–14 years of age). Self-report questionnaires and school records were evaluated for socioeconomic and ethnic group differences in patterns of change over 1 year. Overall similarity in changes over time across ethnic groups was found for relatedness, self-definition, and psychological adjustment, although Black and Latino youth reported more overall adjustment difficulties, Black youth reported less positive relationships with parents, and lower SES youth reported less positive peer relationships than others. Ethnic group differences in changes to school adjustment, even after controlling SES, suggested a cultural variation in which often cited declines in school adjustment during middle school characterize White adolescents to a greater degree than Black or Latino adolescents. Ethnicity moderated associations of relatedness and self-definition with psychological and school adjustment such that Black and Latino youth appeared particularly vulnerable to experiences that threaten closeness and trust in relationships. Results pointed to potentially important situational and cultural differences in maladaptive and adaptive developmental processes across ethnicity.