This article presents results from a case study analyzing the process of change for early childhood educators as they engage in a semester-long professional development (PD) experience focused on developing a teacher research agenda related to mathematics instruction. During this PD experience, 11 participants (5 second-grade and 6 third-grade teachers) developed a research question, collected and analyzed data, and used results to inform mathematics instruction. The overarching question guiding this study was: How does an ongoing mathematics PD model focused on developing a teacher research agenda impact the instructional practice of second- and third-grade teachers? Instructional shifts were apparent across participants, but only after building a shared sense of community during PD sessions. (Contains 1 table.)