Programme theory (PT) development can prove challenging, as power dynamics among stakeholders and/or between the evaluator and stakeholders can be hard to navigate. An important part of the PT-development process is navigating the points of knowledge of a programme and merging them to gain accurate insight on the programme and outcomes. This process typically involves inviting the perspectives of different stakeholder groups and consolidating these perspectives in a visual depiction. This article analyses the PT-development process for the STEM + Families programme of the National Parent Teacher Association (NPTA), based in Alexandria, Virginia (United States). This initiative seeks to increase access to, interest in, and understanding of STEM careers and education pathways for all children, and especially girls, children of colour, and children living in low-socioeconomic communities. The article explores how dialogue, challenges and questioning, and reflection on organisational culture within the NPTA were core components of this process and the eventual PT-model development. In particular, this article will focus on how the PT revealed sources of tension and power dynamics, and illustrated the possibilities of and challenges to the evaluation process, from the beginning of the process to report writing. Finally, the article adds to the evaluation field, as it explores the key evaluation competencies and key learnings from the described process, which hold implications for PT-development processes more broadly. Explorations of situational analysis, reflective practice, and the political and contextual environment in which the evaluation is placed emerge as key considerations and essential skill sets in PT development.