There is much evidence to support the occurrence of learning in connection with collaboration, both in face-to-face and online teaching situations, but much less research on how such collaboration develops over the duration of a course. Using Dillenbourg's concepts of "situation," "interactions," "mechanisms," and "effects" as a framework, this study aims to fill that gap by following a group of 47 university students participating in a 15-week online English course for low- to mid-intermediate learners. Data gathered included participants' reflective journals, questionnaires, written assignments, comments posted on Discussion Forums in a Learning Management System, and e-mail exchanges between individual students and the instructor. These were analysed using open, axial, and selective coding. Three different forms of collaboration were identified--reading each other's work, providing feedback, and working in groups. The main points to emerge from the study were the importance of the social aspect of collaboration, of allowing time for collaboration to develop, and the effect of the gradual development of confidence among the students. Patterns of collaboration changed as the group developed a sense of community and mutual trust, with students who initially held back from offering their work for comment gradually posting their work early to encourage feedback from others.