The role of individual feedback in (online) learning has been widely studied by researchers, but collective feedback based on quizzes and its impact on various academic outcomes has been overlooked to date. The aim of the present study was to compare the effects of displaying individual or collective feedback during an online course on students' attitudes (interest in the course), emotions (social comparison threat), and behaviors (engagement and academic performance). A two-hour online learning session was conducted among undergraduate students in psychology (N = 155) to examine the effects of collective or individual feedback using quizzes on academic outcomes. In a control condition, each student received individual feedback from the teacher privately on their own device indicating the correct/incorrect answers to each quiz question. In an experimental condition, collective feedback was given publicly to the whole online class by displaying the distribution of answers by response options to each quiz question via a videoconferencing system which shared the teacher's computer screen. Results showed that students perceived a greater threat of social comparison, and demonstrated lower behavioral engagement and academic performance in the collective than in the individual feedback condition. The opposite effect was found on interest in the course, which was higher when collective feedback based on quizzes was displayed than when it was not. These findings suggest that collective feedback can be considered as a "double-edged sword" generating both positive and negative impacts depending on the type of academic outcomes taken into consideration.