We contribute to the teacher activism literature an understanding of how activist organizations support professionalization processes. We examine how teachers' involvement in a local activist organization counteracts the de-professionalizing reforms of the standards and accountability movement and fosters the professionalization of teaching. Our findings suggest that the structures of the activist organization provide opportunities for teachers to create and maintain collective knowledge for curricula and practice, sustain their professional commitments to social justice, and build confidence that promotes voice in educational decision-making. We discuss implications for teacher professionalization and identify the need for future studies on the role of teacher activist organizations on teachers, teaching, and the profession.