Studies that employed activity theory as a theoretical lens for exploring computer-mediated interaction have not adopted social media as their object of study. However, social media provides lecturers with personalised learning environments for diagnostic and prognostic assessments of student mastery of content and deep learning. The integration of "Facebook" into educators' pedagogical intentions potentially scaffolds students cognitively, leverages their understanding of content and ameliorates limited mediated learning experiences. Using activity theory as an interpretive framework and a multi-method data construction process involving in-depth semi-structured interviews, in-class observations, post observation debriefing and data mining of student and lecturer-generated "Facebook" postings, the study explored "Facebook's" potential to scaffold student cogitative processes and promote academic engagement. Findings suggest that the academic value of "Facebook" is contingent upon the extent of its integration into the pedagogical design of courses, student academic maturity and their level of ICT competence. The unintended effects of "Facebook" were its reproduction of peer-based academic hierarchies, and its revelation of cognitive tensions and power differentials between academically gifted and cognitively challenged learners during lectures. (Contains 2 tables and 3 figures.)