This study examines the evidence for the effectiveness of professional development using a sample of ten elementary school teachers. These teachers were part of a larger intervention study that investigated the impact of a teaching model, Dynamic Pedagogy on student mathematics achievement. Positive results were obtained from the analysis of three sources of data: a teacher questionnaire about their professional development experiences, a rubric that rated teachers' classroom practice and students' test scores. Results are discussed in terms of the design features of a professional development program that are conducive to improvement in teacher knowledge and their subsequent classroom practice. (Contains 4 tables.)