For a policy maker promoting the end of a harmful tradition, conformist social influence is a compelling mechanism. If an intervention convinces enough people to abandon the tradition, this can spill over and induce others to follow. A key objective is thus to activate spillovers and amplify an intervention’s effects. With female genital cutting as a motivating example, we develop empirically informed analytical and simulation models to examine this idea. Even if conformity pervades decision making, spillovers can range from irrelevant to indispensable. Our analysis highlights three considerations. First, ordinary forms of individual heterogeneity can severely limit spillovers, and understanding the heterogeneity in a population is essential. Second, although interventions often target biased samples of the population, targeting a representative sample is a more robust approach to spillovers. Finally, if the harmful tradition contributes to group identity, spillovers can hinge critically on disrupting the link between identity and tradition.