This study investigated how the use of structured participation, specifically group presentation roles, supported more equitable participation in doing and learning mathematics. We analyzed videos of two lessons focused on radius, diameter, circumference, and area of circles in which students worked in small groups in a STEM project-based geometry class. Students' mathematics learning was assessed by the teacher through a group presentation where students were assigned individual presentation roles. We identified themes related to access and participation in small group and whole class interactions during this problem-focused lesson and found nuanced differences in both access and participation when compared to students' typical involvement in the more common unit-wide project-based tasks. Findings provide insights into effective uses of structured participation for both group work and whole class interactions to support more equitable doing and learning of mathematics in high school classrooms. [For the complete proceedings, see ED606556.]