The aim is to investigate the effects of delivering group-based personalized teaching via an electronic performance support system (EPSS) in an online medical informatics course on medical students' academic achievement and community of inquiry levels. The basic working principle of EPSS is to provide the most appropriate teaching methods to the educator, according to the students' variables and learning outcomes. The research design of this study involved a quasi-experimental pretest-posttest design with a control group and the qualitative research method of answers to follow-up questions. While the students in the experimental group were taught various teaching approaches (flipped classroom, brain storming, case-based learning, debate and think-pair-share), the students in the control group were taught directly by online lessons according to direct instruction method. It was seen that the experimental procedure had a positive effect on both the academic achievement and community of inquiry levels of the experimental group compared to the control group. Besides, students in the experimental group reported that the lessons were more effective when they were enjoyable, motivating, focused on discussion and research, and were taught through cases. The group personalized teaching method used in this study could be a guide for future studies.