Peer instruction (PI) involves students answering questions and peer discussion learning activities. PI can enhance student performance and engagement in classroom instruction. However, some students do not engage in the discussions. This study proposes two mechanisms, discussion partner assignment and accountability scoring mechanisms, to form positive interdependence among students and individual accountability for each student to promote student discussions in PI. The evaluation results show that the student discussion rate with the promoting mechanisms is significantly higher than the rate without the mechanisms. The results from the questionnaire reveal that the mechanisms form positive interdependence and individual accountability to promote students to engage in the discussions.