Children who witness bullying often do not defend victims. Bystanders might be reticent to intervene because they are stuck in “social dilemmas.” Social dilemmas are situations in which individuals make decisions based on self‐interest due to their lack of confidence that others will join with them in decisions that benefit the collective. In this study, the social dilemmas concept, which comes from game theory and social psychology, was applied to bullying for the first time. A total of 292 middle school students at a private residential school in the United States completed surveys about their bullying‐related experiences within their residences of 10 to 12 students of the same gender. Multilevel modeling was employed to assess if and how attitudes, group norms, and social dilemmas predict behavior in bullying situations. The findings suggested that both individual and group factors were associated with behavior in bullying situations and that attitudes, group norms, and social dilemmas each made a unique contribution to predicting behavior in bullying situations. Aggr. Behav. 9999:XX–XX, 2014. © 2015 Wiley Periodicals, Inc.