A major challenge facing the online translation instructor is to design learning opportunities that encourage communication and the sharing of ideas between students. This article asks how such group interaction may be facilitated and evaluates, in particular the impact of task structure on student interaction in an online translation exercise module. Drawing on an empirical study carried out at Dublin City University during the academic year 2003/14, the article compares levels of intermessage referencing, the number and size of message clusters, and extent and type of cognitive presence evident in messages posted by students given three different types of task structure: those involving discussion groups, cooperative groups and collaborative groups. The article concludes that online interaction is most successful in discussion groups, followed in order of positive outcomes by cooperative groups and collaborative groups.