Prior studies of social-norms interventions have focused on nudging behavior in noncompetitive settings. This research evaluates such interventions in competitive environments, for example, a class with a competitive grading policy. Field experiments on a learning management system show that providing descriptive information about peers’ behavior has mixed effects in reducing procrastination and improving performance outcomes. Specifically, the effects are moderated by individual characteristics and contextual variables. First, peer information interventions are more effective for males, and the effects are stronger in a male-majority environment than in a female-majority environment. These findings differ from prior studies of social-norms interventions conducted in noncompetitive settings, in which females are found to be more responsive to interventions. Gender differences in our competitive settings can be explained by males’ and females’ differential preferences for competition: males are more competitive-oriented and thus are more responsive to peer information in competitive environments. Second, we find that individuals who are in great need of interventions, that is, those with poor past behavior and performance, are also more likely to benefit from peer information interventions, suggesting that peer information interventions motivate positive change. This study highlights the heterogeneous effects of peer information interventions and has implications for targeted interventions.