This mixed-methods cluster-randomized controlled trial examines the impact of a teacher-training program that aimed to promote positive gender socialization in the conflict-affected region of Karamoja, Uganda. The theory of change suggests that the education system and teachers can play critical roles in promoting positive gender roles and gender equality, which has important implications for peacebuilding. Our study found evidence that the program positively influenced teachers' knowledge about the difference between gender and sex, and their attitudes toward gender roles and gender identity. We found no quantitative evidence for any short-term change in teachers' practices as a result of the program, nor did we find quantitative evidence of effects from a complementary, randomly assigned text-message intervention meant to reinforce the information delivered during the training. Qualitative research suggested that, while teachers adopted basic practices taught in the training, they were unready or unable to adopt more complex practices. The main implication is that training can influence teachers' knowledge and attitudes on gender equality, but traditional gender norms can be a barrier to changing behavior in the short term. A further implication is the importance of involving the community to create enabling environments in which new ideas about gender equality can be accepted and translated into practice.