Key Social Norms Take-Aways This study underscores that changing social norms is possible but complex. Interventions prompted discussion and shifted some attitudes but also deepened divisions. Gender and power hierarchies remained largely intact, and future programs must anticipate resistance and support collective norm change. Objectives: This study evaluated whether social norms interventions and economic incentives could reduce child marriage in Ethiopia. It aimed to assess the effectiveness of these approaches not only in reducing early marriage rates but also in shifting related social norms and gender attitudes. Methods: The study used a quasi-experimental design with a difference-in-differences approach and inverse probability weighting. Baseline (2012) and follow-up (2014) surveys were conducted in the Amhara region, covering over 2,500 households at baseline and 694 at follow-up. Data included responses from parents and adolescent girls on marriage, education, gender norms, and household dynamics. Intervention Details: Two types of interventions were tested. The “expansion” arm included community conversations, school clubs, and campaigns led by peer educators and local influencers. The “intensive” arm added economic incentives: school materials for girls and access to financial literacy training and a revolving loan fund for caregivers, conditional on girls staying in school and unmarried. Influential community members were trained to lead discussions challenging harmful practices. Results: Both intervention arms reduced the probability of child marriage among girls aged 8–17 by 4–7 percentage points. While the intensive arm showed slightly greater reductions, the difference was not statistically significant. Spillover effects included increased household decision-making power for mothers and greater control over how they spent their income. However, the interventions had no significant impact on school enrollment or grade completion, and in some cases may have worsened attitudes about women’s rights. Conclusions: The interventions effectively reduced child marriage but had limited success in shifting broader social and gender norms. Education outcomes remained unchanged, and backlash was observed, especially around gender roles.