Groups such as committees or boards make many important decisions within organizations. Many of these decisions affect external parties. This paper uses an experimental approach to study how the gender composition of three-person groups affects choices and beliefs in a Coordination game with selfish and prosocial equilibria. We find that the social preferences of group members are a key determinant of the group’s coordination choice. Controlling for social preferences of the group, groups with more women are more likely to make choices that are kinder to external parties. Both men and women believe that women will make kinder choices more frequently. Groups comprised of all men are expected to make 18 percentage points fewer kind choices than groups of all women. Men are also expected to be 9 percentage points less kind than women overall. These results have implications for public policies intended to increase gender diversity and women’s representation on decision-making committees in the corporate sector, in politics, and in academia.