My research explores teacher cognition and the process of learning to teach, with an emphasis on changes in novice and experienced teachers' knowledge and beliefs about teaching, learning, subject matter, and their classroom practices. I am particularly interested in factors that facilitate and hinder teachers' learning of reform-based practices, and in policies and practices that can support teacher change. Currently, my research team is studying the impact of the Problem-Solving Cycle -- a professional development program for middle school mathematics teachers that we designed -- on teachers’ professional community and their knowledge, beliefs, and instructional practices.