Computer-mediated communication (CMC) tools can be used to integrate time-intensive tasks, such as case study analyses, more easily into formal learning environments. How students talk together online in CMC environments is an area that has not yet been thoroughly investigated. This paper extends findings from a previous study by comparing two groups of preservice teachers analyzing cases in a synchronous and asynchronous environment. A case study and computer-mediated discourse analysis approach was taken to make sense of the discussion transcripts and student reflections. Booth and Hulten’s (2003) taxonomy of learning contributions is used as an analysis framework. Students made more participatory moves to establish presence in asynchronous environments and more interactive moves in synchronous environments. Reflective contributions were made in both environments, with few learning moves made in either. Students participated asymmetrically in both modes. The interplay between types of contributions, affordances of each mode, student preferences and student epistemological beliefs is explored, with implications for the design and analysis of case discussion tasks in CMC environments.