The purpose of this study was to use a narrative approach to investigate the process undertaken by a mathematics teacher as she implemented a mathematics inquiry teaching program. Data collection methods included unstructured interviews, videotaped classroom observations, videotaped group meetings, and the teacher's and researcher's reflective notes. By means of a narrative analysis, an emplotment was developed to depict changes in the teacher's beliefs and practices. The research findings showed that the teacher's initial beliefs and practices were founded upon her former learning experiences and the influence of her family. Participation in the activities of a professional development research group, which included reviewing recent literature, inspecting and learning from an exemplary teacher's instruction, reflecting on each other's videotaped classroom teaching, and interacting with peers, seemed to encourage the case teacher to change her beliefs and practices.