Meaningful and effective training and professional development programs for teachers are key to the improvement of teaching practices in our schools. In this paper, the authors offer a meta-synthesis of the literature on the role of reflection for mathematics and science teachers within the context of professional development. The authors frame this review using Desimone's core components of professional development, a research-based framework emphasizing components tied to positive outcomes (content focus, active learning, coherence, duration, and collective participation). A synthesis of literature in this area shows that few training and professional development programs include all five components of Desimone's core conceptual framework for effective professional development linked to positive outcomes. Further, the authors find in their review that increased contact hours included in a professional development program produce an increase in frequency, duration, and depth of reflective practice for teachers.