The purpose of this study was to examine fidelity of peer mediation and its role in improving students’ oral English communication skills at Debre-Berhan University. A Communicative English Skills class was randomly selected as a study group. From this class, high- and medium together with low performing students in oral English communication skills were identified as peer mediators (N=15) and mediatees (N=61), respectively. The mediatees were categorized into medium and low achieving peer groups, each of which comprised five members, including one peer mediator assigned randomly to the group. During a three-week teacher-led session, the peer groups were trained in the peer mediation procedure enhancing such aspects of oral abilities as organization of related bits of information, succession of events and description of individual qualities in personal introduction. The findings revealed that there was an acceptable level of agreement between both the peer mediators and the mediatees on fidelity of the peer mediation as they rated the fidelity checklist. Pre-to post-test oral communication scores significantly improved for low and medium achievers as a result of the peer mediation. Based on the findings, recommendations were made for purposes of examining sustained practicality of peer mediation toward improving students’ learning and performance in oral English communication skills.