This study examines teacher leaders who engaged in a professional development program focused on conducting action research related to mathematics instruction. More specifically the study focused on how teacher leaders described their experience with a collaborative-structured action research process as part of a professional development program and how they described the influence of the experience on their practice. Using an embedded multiple-case design of case study, multiple sources of data were collected and analyzed from this year-long study of eight teacher leaders from diverse contexts, as they developed and implemented action research projects. Findings suggest that participation in the professional development project, and accompanying study, influenced the practices of the teacher leaders in several ways including an increase in their intentionality with decision making, set them on a trajectory toward seeking continual improvement, and supported them to develop increased knowledge. The teacher leaders considered the structural aspects of learning to conduct research and opportunities for collaboration to support their experience. Implications are provided to describe the possible affordances and opportunities for consideration for implementation of action research as professional learning.