From early in development, humans show a strong preference for members of their own groups, even in so-called minimal (i.e., arbitrary and unfamiliar) groups, leading to tremendous negative consequences such as outgroup discrimination and derogation. A better understanding of the underlying processes driving humans’ group mindedness is an important first step toward fighting discrimination and inequal- ity on a bigger level. Based on the assumption that minimal group allocation elicits the anticipation of future within-group cooperation, which in turn elicits ingroup preference, we investigate whether chang- ing participants’ anticipation from within-group cooperation to between-group cooperation reduces their ingroup bias. In the present set of five studies (overall N = 465) we test this claim in two different popu- lations (children and adults), in two different countries (United States and Germany), and in two kinds of groups (minimal and social group based on gender). Results confirm that changing participants’ anticipation of who they will cooperate with from ingroup to outgroup members significantly reduces their ingroup bias in minimal groups, though not for gender, a noncoalitional group. In summary, these experiments provide robust evidence for the hypothesis that children and adults encode minimal group membership as a marker for future collaboration. They show that experimentally manipulating this ex- pectation can eliminate their minimal ingroup bias. This study sheds light on the underlying cognitive processes in intergroup behavior throughout development and opens up new avenues for research on reducing ingroup bias and discrimination.