The study adopted a sequential mixed-methods approach to investigate student teachers' learner agency in a teamwork setting at Qatar University. In the qualitative phase, a total of 10 student teachers enrolled in a course adopting a STEAM pedagogical approach participated in in-depth interviews. Qualitative analysis identified seven sources for practicing learner agency in teams. Using this data, the Learner Agency in Teamwork Settings survey was constructed. The survey was distributed to 108 student teachers taking the same course, which utilized an inquiry, problem solving, and digital-based learning design. Using exploratory and confirmatory factor analyses, four factors emerged, including: interest and motivation, teamwork self-efficacy, socio-cultural support, and team support. The findings have important educational implications for promoting student teachers' agency in similar educational contexts.