New experiences, challenges, and opportunities inherent in biographical transitions are expected to foster the psychosocial development of individuals. Our study investigated, first, developmental gains in children's language competence, social support seeking, and self control following the transitions to kindergarten and school; second, whether native Germans, ethnic German repatriates, Russian Jewish and Turkish migrants differed in developmental gains following these transitions; and third, whether differences in mother's education, financial standing, or network contacts accounted for ethnic group differences in developmental gains. In total, 111 mothers of kindergarten-aged and 179 mothers of school-aged children were interviewed twice, before and after the respective transition, with a one-year-interval. Results showed that, according to mothers' reports, children increased in language competence and self control after both transitions. The increase for some outcomes varied, however, between ethnic groups and was accounted for by differences in maternal education. Results underscore the importance of immigrants' education for the positive development of their offspring and of institutional opportunities in compensating for early disadvantages.