We examined whether two interpersonal processes, self-disclosure and affirmation of ideal self, mediated the relationship between cross-ethnic friendships and psychological well-being and academic outcomes. We conducted a cross-sectional survey with 484 secondary school children (243 White European, 241 South Asian British; M-age=11.10, 220 boys, 264 girls) recruited from 35 multiethnic classrooms. Results of multilevel structural equation modeling revealed mediational effects of self-disclosure between cross-ethnic friendships and psychological well-being for only South Asian children. Affirmation also mediated the association between cross-ethnic friendships and both psychological well-being and academic outcomes for South Asian children. For White European children, affirmation mediated the association between cross-ethnic friendships and psychological well-being. Further analyses demonstrated that self-disclosure resulting from cross-ethnic friendship quality facilitated affirmation, which in turn promoted both sets of outcomes. Findings demonstrate that cross-ethnic friendships in multiethnic settings contribute to well-being through the generation of positive interpersonal processes.