This study described the experiences of a group of seven sixth-grade teachers and the participation of their emergent bilingual students (EBs) during the implementation of an instructional protocol designed to provide students with opportunities to engage in mathematical reasoning through discourse. The Discursive Mathematics Protocol (DMP) is supported by socio-constructivist theories and incorporates equitable teaching practices in mathematics to provide EBs with opportunities to develop mathematical reasoning and language competencies. This descriptive case study provides a review of the literature on mathematical reasoning, the DMP, teaching practices to support students' development of mathematical reasoning, and professional development strategies to support teachers in learning about mathematical reasoning and implementing the DMP. A cyclical methodological approach was implemented to gather data from three lessons with the purpose to analyze EBs' mathematical reasoning, teaching practices, as well as the teachers' characterizations of their experiences learning and using the DMP during problem-solving lessons to help support their EBs' mathematical reasoning development. The findings provide evidence of the positive impact that the DMP has on teachers' and students' learning. Teachers had opportunities to focus on students' learning, implement the teaching practices promoted in the DMP, and identify areas of improvement by changing their conceptions and practices. Throughout the implementation of the different tasks, teachers engaged students in mathematical reasoning. Students also advanced their reasoning and then were able to use and connect different mathematical representations and explain and justify their ideas. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]