There is a need for professional development programs that support effective teaching practices in mathematics, which are consistent with recommendations in reform documents and emphasize students’ reasoning and understanding. However, the nature of such programs is open for debate. What teachers should know to teach mathematics for reasoning and understanding and what environments support teachers’ learning of such knowledge remain open questions. This study will report on the experience of seven in-service elementary and middle school mathematics teachers who participated as interns in a three-year afterschool classrooms-based research project that examined how students build mathematical ideas and reason while working collaboratively on challenging tasks selected for several content strands. The teachers’ participation in the project as part of a professional development program aimed at promoting teaching that supports reasoning and understanding in mathematics classrooms. In the first year, the teachers observed researchers lead research sessions with a cohort of sixth-grade students. In the second year, partner teachers led similar sessions with a new cohort of sixth-grade students implementing the same content while other teachers, researchers, and graduate students observed. In the third year, the teachers and researchers jointly analyzed the data collected in the project, and disseminated findings in research conferences. There were also debriefing meetings at the end of each research session involving teachers and researchers which focused on reflections, discussions, and challenges in supporting students’ mathematical reasoning. Based on a qualitative analysis of teachers’ actions in research sessions and their reflections in debriefing meetings, this study will show how participation in the afterschool project supported teachers’ development of effective teaching practices helping them notice and implement teaching strategies that promote students’ mathematical reasoning and understanding. This study will describe the teaching practices and examine the conditions of the afterschool program that supported teachers’ development of the strategies. The results show that engaging teachers in research on students’ development of mathematical ideas and reasoning can be an effective way of promoting effective teaching practices in mathematics classrooms.

Keywords: Effective Teaching practices in Mathematics, Professional Development, Teacher Learning, Development of Mathematical Ideas and Reasoning, Teachers as Researchers.