This holistic, mixed-methods action research case study aimed to determine the influence of professional development on participants' mathematical teaching practices and how the changes influenced students' opportunities for discourse. In this two-year study, participants engaged in two professional development phases and implemented new conceptual teaching practices. Quantitative data were collected through surveys and observations. Qualitative data were collected through observations and interviews. Phase-one findings showed that while teachers changed their practices, they were not proficient in conceptual and discourse-based teaching practices. A second phase of professional development occurred using a Community of Practice model. Phase-two findings showed conceptual teaching practices were now a regular part of participants' routines, and students were provided with multiple opportunities for dialogic discourse throughout their school day. Findings from this study add to the growing body of research on the need for contextualized, ongoing professional development to implement conceptual-based mathematical practices. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]