Collective Impact Evaluation is growing in popularity but can take time to initiate. Beyond bringing organizations together as a coalition or community, evaluators must create buy-in for collective impact measurement efforts. This means finding a common thread across organizations to collect and make meaning of data together. Challenges arise, especially with a national audience and dispersed activities. Aligning coalition leaders, funders, service providers, and program staff becomes essential. One tool that can be helpful in this approach is the Theory of Change. This session will explore how engaging with a Theory of Change helped initiate evaluation efforts with the Hidden Helpers Coalition. Presenters will describe how the outcome mapping process led to a clearer understanding of shared goals, short-term outcomes, and a foundation for understanding of population-level impact. Presenters will share strategies for having successful conversations with diverse stakeholders, techniques to initiate discussions about outcomes, and questions that guide outcome-focused dialogues.