This dissertation study examines K-8 mathematics teacher agency and learning within a research-practice partnership (RPP) context. The study is framed by three primary research questions: (a) How is teacher agency enacted within an RPP? (b) What do teachers perceive they are learning from their participation in an RPP? and (c) How is teacher agency connected to teacher learning in an RPP context? An ecological framework for teacher agency and situated learning theory about teacher learning were both utilized to frame the questions and analyses. Furthermore, case study methodology was employed to closely examine K-8 mathematics teachers’ participation and experience in a co-design team in one school district. Multiple types of data were collected including semi-structured interviews, meeting observations, and related documents for two years. Additionally, those data sources were supplemented with a targeted set of semi-structured interviews about teacher agency and teacher learning. The data were analyzed using primarily qualitative methods, and specifically, with coding approaches associated with grounded theory. The study’s findings indicate that the quality of teacher agency enactment changed over time, and there are multiple factors that potentially impacted their participation. Amid the teachers’ involvement in the RPP, teacher learning occurred not just about mathematics teaching but also about other areas such as leadership, collaborative abilities, and understanding of the iterative process of designing teacher support, which are all crucial components of capacity building for creating sustainable learning opportunities even after the partnership with the university. Possible connections between teacher agency and learning are discussed, and implications for inviting teachers to the RPP are offered