Purpose: A social learning management system (social LMS) is a tool which favors social interactions and allows scholastic institutions to supervise and guide the learning process. The inclusion of the social feature to a "normal" LMS leads to the creation of educational social networks (EduSN), where the students interact and learn. The advantages derived from an augmented student-student interaction are counterbalanced by the difficulty to control the quality of the information. For this reason, the purpose of this study is to understand who is a source of reliable and high quality knowledge among the students. Design/methodology/approach: The authors suggest to categorize the actions of the students within roles where the most natural formal role regards the academic performance of a student. Within the EduSN, a student can produce information--social contribution role--and evaluate the contents provided by other peers-- social judge role. Aside from the free production, it provides a publication workflow which allows to certify and improve the quality of the material created by the peers. The publication workflow naturally leads to the definition of two additional roles--the editorial and leader roles. Findings: The paper provides a new definition of expertise within a social LMS, where the key feature of an expert in an EduSN is to improve the quality and quantity of the knowledge flow in the network. The indicators which stem from the roles naturally lead to the definition of the figure of the anti-expert. Originality/value: At variance with the spectrum of values usually associated with expertise (which ranges from novice to expert), in a social LMS, it becomes clear the need of the definition of a new figure--the anti-expert, who has a negative impact on the overall knowledge flow of the EduSN.