Group interaction is a key component of group-based learning. However, its implementation in educational practice is inefficient. Previous studies have discussed the use of concept mapping as a knowledge representation tool to facilitate group communication and trigger shared cognition. Deficiencies in the collaborative use of concept mapping have also been recognized, mainly related to the coordination of group activities, especially in distance groups. Previous studies have proposed roles with different functions to coordinate group activities in concept mapping. However, there is no systematic view of role assignment and there have been no empirical studies examining the effectiveness of the role-based approach. This study addressed this research gap by assigning the roles of cognitive leader, metacognitive leader, and socio-emotional leader to students in concept mapping mediated small group learning. The study demonstrated the design and implementation of the role-based approach in an online learning environment. The evaluation results evidenced the feasibility of the role-based approach and its usefulness in improving socio-emotional experiences in small group learning. The insignificant effects of the approach on cognitive and metacognitive aspects of group interaction indicated the need to investigate the strategies for role assignment and implementation of role duties to determine whether and how these issues might affect the effectiveness of the role-based approach.