Although an open classroom climate for discussion has been demonstrated to benefit students' civic outcomes, individual differences in its effectiveness have not been fully investigated. In this study, we hypothesized that the positive effects of an open classroom climate for discussion would be moderated by positive teacher-student relationships. Based on Taiwanese data (N = 3953, M[subscript age] = 14.11, 52% male) compiled by the International Civic and Citizenship Education Study in 2016, this study examined how an open classroom climate for discussion and teacher-student relationships jointly predicted students' civic knowledge and expected electoral participation. The results of multi-level modeling reveal a cross-level interaction effect between an open classroom climate for discussion (as the classroom-level predictor) and students' perception of teacher-student relationships (as the student-level moderator). Specifically, students who had less positive relationships with their teachers benefited more from an open classroom climate for discussions in terms of civic outcomes compared to those who had more positive relationships with their teachers. These findings have important implications for citizenship education.