This chapter shares insights from a research project used to develop a bespoke evaluation framework for Project X, a creative programme for young people experiencing mental health challenges in Aotearoa New Zealand. Project X was under pressure to produce evidence of impact using outcome and evaluation frameworks that compromised the purpose, integrity, and potential of the project. As part of a University of Auckland PhD research study Project X embarked on participatory research designed to develop an evaluative framework that could articulate ‘impacts’ in ways that were evidence-informed, aligned with participants’ aspirations, and reflective of the unique contribution of arts-based approaches. Using a Theory of Change (ToC) approach, our research facilitated in-depth understanding about Project X’s potential to achieve desired outcomes informed by the diverse perspectives of young people and partner organisations (spanning arts, health, education, and culture). Ultimately, we produced a principle-based practice framework grounded in the context of place, our shared perspectives, and multiple knowledge systems. These include lived experience, practitioner expertise, Mātauranga Māori (Māori knowledge), research, and evidence. This chapter shares insights we believe will be useful to other organisations working in similar contexts or addressing relevant challenges around evaluation.