Computer-mediated communication (CMC) is rapidly emerging as a new modality of educational delivery, either as an alternative to face-to-face contact or as an additional resource to enhance and extend existing pedagogical processes. Computer-mediated technologies produce social environments that are different from traditional classrooms. As such, research is needed to review and redefine the character of online participation/interactivity, as well as to explore the nature of interpersonal aspects of online group learning. Interaction is considered a key issue in online knowledge building processes, while interpersonal issues tend to be regarded as disruptive. In this study, interactivity is viewed both as the degree of intermessage reference and as a personal attitude among participants. Thus, the type of interaction is considered as related to the degree of interpersonal or socioemotional content. The main purposes of this ex-post-facto, longitudinal case study study are to evaluate the amount and type of interaction and interpersonal content in messages posted among online postgraduate students, as well as to determine if there is an association between both variables. It focuses on a continuing interaction of a small group discussing on academic forums equally spaced throughout three semesters, on asynchronous, unstructured discussions based on reflection questions posed by a tutor. The study involves the same natural group working on multiple tasks of the same task type through an extended period of time and measured at three different points in its history. The online group relationship is considered as one homogeneous, holistic interaction. The results indicate that fostering appraisal, support, humor, and inquiry, iv while stimulating healthy opposition based upon personal experiences and factual information ensures a greater dose of reactivity/interactivity. This may increase significant participation and expand the depth of discussion. Moreover, aiding effective tutoring, mentoring and coaching of online groups may help bringing about the full potential of the medium and contribute to the development and maintenance of effective group exchanges. Finally, regulating the complexity of interactions and fostering the development of a cohesive group of participants may render more controlled patterns of online behavior and improve collective learning.