The principal contradiction of online distance education is the disparity that exists between economies of scale and the new interactive capabilities of digital technologies. This is particularly felt where mega-universities in developing countries seek to make better use of these affordances while at the same time protecting their economies of scale. This article interprets the course design of the University of South Africa's signature courses (SCs) within this framework. The SCs combine a high class size--one teaching assistant (TA) supports 200 students--with frequent interaction enforced by the high number of deliverables (ten assignments per semester). This leads to a high marking workload for TAs reducing the time for facilitating online discussion. How this contradiction plays out is further examined with empirical data taken from one particular SC. The quantitative data analysis (based on simple word and message counts of students and TAs) is interpreted in the light of the semi-structured interviews with TAs.