From an intergroup relations perspective, relative group size is associated with the quantity and quality of intergroup contact: more positive contact (i.e., intergroup friendship) supports, and negative contact (i.e., experienced discrimination) hampers, minority identity, and school success. Accordingly, we examined intergroup contact as the process through which perceived relative proportions of minority and majority students in school affected minority success (i.e., school performance, satisfaction, and self-efficacy). Turkish minorities (N = 1,060) were compared in four Austrian and Belgian cities which differ in their typical school ethnic composition. Across cities, minority experiences of intergroup contact fully mediated the impact of perceived relative group size on school success. As expected, higher minority presence impaired school success through restricting intergroup friendship and increasing experienced discrimination. The association between minority presence and discrimination was curvilinear, however, so that schools where minority students predominated offered some protection from discrimination. To conclude, the comparative findings reveal positive and negative intergroup contact as key processes that jointly explain when and how higher proportions of minority students affect school success.