This study examined the relations between majority/minority group membership and cross-cultural acceptance, and their linkage to school adjustment. A total of 2,016 students (ethnic minority [EM]: 51%; boys: 50%) at Grades 2, 5, 8, and 11 from 15 schools in Hong Kong participated in the study. These schools were either of low (below 30%) or high EM concentrations (over 70%). EM students at low-EM-concentration schools and Chinese students at high-EM-concentration schools both belonged to the minority groups in their respective schools. Moderated mediation analyses showed that being the numerical minority in school predicted higher school engagement and more positive affect. The associations between numerical group membership and adjustment outcomes were each mediated by the intention to accept outgroup members. In other words, higher cross-cultural acceptance was found among students who were themselves the minority in school, and stronger outgroup acceptance, in turn, predicted better adjustment. Copyright © 2020 The Author(s).