Calculus differential is the basis of mathematics before entering the level of further mathematics, which has a high analysis level. Students have difficulty understanding concepts and have not been able to analyze/predict/realize (self-efficacy) that impact challenges in working on calculus problems. On the other hand, technology has been developed in education. This research compared conventional flipped classrooms and peer teaching flipped classrooms. This research investigated the differences in students' conceptual understanding and self-efficacy in both classes in terms of majors' background and prior achievement level. This research used a nonequivalent-groups pretest and posttest design. The data was collected using test and questionnaire. The ANCOVA results showed that peer teaching flipped method was better than the conventional flipped classroom method in terms of students' conceptual understanding and self-efficacy. Moreover, self-efficacy had a positive correlation with conceptual understanding in both methods. Furthermore, the students' prior achievement level influenced students' conceptual understanding and self-efficacy, while students' majors background influenced students' self-efficacy only.