The sample consisted of 225 boys and 223 girls (ages 11-14 at the first assessment) recruited from the 6th and 7th grades of a large, public middle school in a socioeconomically and ethnically diverse metropolitan community. The student population was composed of approximately 42 percent White, 29 percent Black, 27 percent Latino, and 3 percent Asian. All of the self-report measures used in this study have shown evidence of reliability and validity in previous research with multiethnic samples. Self-report questionnaires and school records were assessed for socioeconomic and ethnic group differences in patterns of change over 1 year. Overall, there was similarity in changes over time across ethnic groups in the areas of relatedness, self-definition, and psychological adjustment; however, Black and Latino youth reported more overall adjustment difficulties. Black youth reported less positive relationships with parents, and youth from families with lower socioeconomic status reported less positive peer relationships than others. There were differences in changes in school adjustment among ethnic groups, even after controlling for socioeconomic status. Grades declined significantly for White students and marginally for Latino adolescents, but they increased slightly for Black adolescents. Future research should examine whether ethnic group differences reflect the effects of unique strategies developed by ethnic minorities for adjusting to the academic demands of middle school. Ethnicity was found to moderate associations of relatedness and self-definition with psychological and school adjustment, such that Black and Latino youth were particularly vulnerable to experiences that threaten closeness and trust in relationships. Overall, these findings indicate significant situational and cultural differences in maladaptive and adaptive development processes across ethnicity. Study limitations and directions for future research are discussed. 6 tables, 2 figures, and 91 references