Within the literature on the relation between membership in voluntary associations and tolerance, three theoretical perspectives can be distinguished. The socialization perspective assumes that the interaction within association leads to higher levels of tolerance; the self-selection perspective suggests that tolerant actors are more likely to join associations; while the selection and adaption model predicts that the group culture within an association will have a specific effect on members’ attitudes. We use a two-year panel study among Belgian adolescents to ascertain the empirical merits of these three approaches. Results show that not all associations have an effect on the reduction of prejudice, but that this effect is limited to specific associations. A structural equation model furthermore suggests that socialization effects are significantly stronger than self-selection effects. As such, this analysis of panel data lends support to the selection and adaptation model.