Peer Instruction (PI) is a widely used student-centered pedagogy, but one that is used differently by different instructors. While all PI instructors survey their students with conceptual questions, some do not allow students to discuss with peers. We studied the effect of peer discussion by polling three groups of students (N = 86) twice on the same set of nine conceptual questions. The three groups differed in the tasks assigned between the first and second poll: the first group discussed, the second reflected in silence, and the third was distracted so they could neither reflect nor discuss. Comparing score changes between the first and second poll, we find minimal increases in the distraction condition (3%), sizable increases in the reflection condition (10%), and significantly larger increases in the peer discussion condition (21%). We also examined the effect of committing to an answer before peer discussion and reaching a consensus afterward. We compared a lecture-based control section to three variations of PI that differed in their requirement to commit to an answer or reach consensus (N = 108). We find that all PI groups achieve greater conceptual learning and traditional problem solving than lecture-based instruction. We find one difference between these groups: the absence of consensus building is related to a significant decrease in expert views and beliefs. Our findings can therefore be used to make two recommendations: always use peer discussions and consider asking students to reach a consensus before re-polling.

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