Despite the prevalence of professional development in schools and the variability in its implementation, little research has been conducted on how professional development makes its way into the classroom. Even when teachers participate in high-quality professional development, there remains a large and often undocumented variability in how teachers make use of ideas learned. Therefore, educational researchers and professional developers need to better understand the dilemmas and choices teachers face in making use of learned practices. The goal of this particular study was to understand the relationships between professional development and classroom practice. The authors looked at the ways teachers participated in the communities and their identities as teachers of mathematics across the communities. Examining teachers in both settings allowed for a comparative analysis of teachers' participation in and identities around their professional development and classroom community. To highlight the ways in which identity help them make sense of the relationship, they focus on detailing the participation and identities of two of the particular workgroup teachers. (Contains 2 notes.)