This project convened experts and practitioners in the areas of program evaluation, radicalization to violent extremism, and social media analytics in order to generate and integrate scientifically derived knowledge into strategies for effective prevention and intervention against domestic radicalization and violent extremism in the United States. More specifically, we generated substantive evaluation data, which can be used by practitioners and policy makers to enhance the creation and dissemination of effective counter-narratives for reducing the threat of ideologically-motivated violence in the US. We used a mixed-methods approach to evaluate an existing nationwide initiative, Peer-to-Peer (P2P): Challenging Extremism, which aims at engaging youth in countering violent extremism in schools and online arenas. The project had four specific objectives: 1) Evaluate the content and dissemination of the P2P Initiative social media products, 2) evaluate the impact of the P2P Initiative on youth engaged in its development, 3) evaluate the impact of youth exposure to the P2P educational activities, and 4) assess the drivers of success and barriers in the implementation of the initiative. To complete these objectives, the following research phases were conducted: A secondary review of 150 P2P social media products created between fall 2015 and spring 2017, including data on end-users interactivity. Phone and in-person group interviews with faculty and students engaged in the P2P Initiative. A prospective cohort study evaluating the impact of the Kombat with Kindness (KWK) campaign on Utah secondary school students, using a pre-post intervention design. A randomized control study evaluating the impact of the Operation 250 (OP250) on Massachusetts secondary school students, using a pre-post intervention design. Phone interviews with faculty who implemented the P2P Initiative.