Group discussion has effectively changed attitudes and behaviors even when individual-targeted messages have been unsuccessful. We propose that discussion is effective because it allows individuals to hear other people endorse the communicator’s message. Students (n = 300) heard the same message about replacing toxic products with nontoxic alternatives; classes were randomly assigned to hear the message delivered as a lecture or via guided group discussion. Analyses indicated that discussion was more effective than lecture, particularly for students who chose their own products. Additional analyses indicated these effects were mediated by students’ perceptions that other students endorsed nontoxics; the presentation style main effect was partially mediated, and the interaction with product choice was fully mediated. Cognitive elaboration did not operate as a mediator, but was related to final attitudes, consistent with views that positive elaboration leads to attitude change. Results support the importance of hearing others’ opinions, and underscore the limited value of individually-oriented persuasive messages about socially motivated behaviors.