This study examined the tensions that surfaced as a result of a teacher's transition from traditional to reform-oriented pedagogy while participating in the Mathematics Teacher Development Project and using the Investigations in Number, Data, and Space curriculum. In particular, the purpose of this study was: (a) to explore the relationship that develops between a teacher's learning in a teacher development project and her implementation of an innovative curriculum as it may influence the resolution of dilemmas that arise as she attempts to reform her practice; and (b) to identify features of the teacher development project and the curriculum that appear to have impacted the teacher's practice. The study was conducted as a case study with a practicing teacher (Maria) who had already taught at the elementary level for 10 years. At the time of the study, Maria participated in the fifth (last) semester of a reform-oriented teacher development program and was using a reform-oriented curriculum for the first time. This study indicates that an effective teacher education program utilized in conjunction with a reform-oriented curriculum provides teachers with learning opportunities that promote the transformation of their traditional ways of teaching. However, their learning creates tensions and dilemmas resulting from specific conflicts (e.g. decision making about the focus of lessons) between their evolving, reform-oriented understandings and the traditional ways to which teachers are accustomed. Contains 22 references. (Author/CCM)