In this article, we share our experiences in mathematics teacher education around professional development for teachers with a focus on student participation as an opportunity to learn. We describe a process through which teacher educators can support teachers in increasing and improving classroom participation opportunities for their students. We present Lesson Activity Bars and Difference in Participation Proportion, complementary tools that quantify and represent student participation in the mathematics classroom. We demonstrate the effectiveness of these tools in supporting teacher growth in the context of a professional growth project for teachers in urban secondary schools. In general, the teachers in this project increased the amounts of active participation they made available to their students. The cases of two teachers are analyzed in detail, using Clarke and Hollingsworth's (2002) Interconnected Model of Professional Growth, to add depth and nuance to our understanding of processes of teacher growth around increasing student participation opportunities in the mathematics classroom.