Previous research has suggested that moral disengagement is strongly associated with bullying and bystander behavior. The current study evaluated the effectiveness of a 5-week classroom-wide bullying intervention, "The Bullying Literature Project-Moral Disengagement Version (BLP-MD)", on moral disengagement and bullying among elementary school students. A quasiexperimental design was used to evaluate the effectiveness of the "BLP-MD". A sample of 84 third grade students (M[subscript age] = 7.93 years, 53.6% female) from four classrooms and their teachers participated in this study. The results revealed significant time by treatment interactions for decreasing both victimization and moral disengagement in treatment classrooms compared to waitlist control classrooms. The program also resulted in improved perception of peer friendships and was rated as having high social validity for both students and their teachers. How to incorporate the "BLP-MD" into the general language arts curriculum to decrease moral disengagement and bullying, and promote positive bystanding is discussed.