Background: The feedback offered to students in audience response systems may enhance conformity bias, while asking closed-type questions alone does not allow students to externalize and elaborate on their knowledge. Objectives: The study explores how writing short justifications and accessing peer justifications as collective feedback could affect students' performance, confidence and opinions in multiple-choice audience response systems that apply the Peer Instruction model of voting/revoting. Methods: For 8 weeks, 98 students, enrolled in an undergraduate course, attended each lecture following a flipped classroom approach. At the beginning of each lecture, students participated in a quiz with eight multiple-choice questions. Four of these questions included a justification form in which students could elaborate on their answers. The students were randomly grouped into two conditions according to the collective feedback they received: the Shared group (n = 54) could see both the percentage each question choice received from the class and the respective peer justifications, while the Unshared group (n = 44) could only see the percentage information. Results: Analysis showed that students in both groups performed significantly better in questions with the justification form being available. Also, the two groups were comparable in terms of performance and self-reported level of confidence suggesting no main effect for making peer justification available. Despite this, students in the Shared group expressed a significantly more positive opinion in the end-of-activity questionnaire in terms of perceived learning gains and the helpfulness of writing justifications for their answers. Take Away: Writing short justifications can have a positive impact on students' academic performance.