Over recent years, educational institutions have been making increasing use of virtual environments to set up collaborative activities for learners. While it is recognized that teachers play an important role in facilitating learner collaboration online, they may not have the necessary skills to do so successfully. Thus, a small-scale professional development programme was set up and piloted by two distance universities. The aims were to develop teachers' experience of online group work, to trial a set of pilot activities that would raise awareness of factors contributing to successful collaborative online activity, and to identify professional development needs in this area. This article reports on the hands-on experience of a group of 20 teachers, examines some of the competences that are needed to successfully collaborate in virtual environments, and presents the skills that teachers need to foster online collaborative learning in the virtual classroom. Quantitative and qualitative data were collected, examining the levels of participation among participants, the collaborative activity of two groups, and teachers' perception of the collaboration that took place. The skills identified include planning and managing the collaboration, designing appropriate activities, giving clear instructions and getting students to negotiate ground rules for participation, moderating at the right level, and choosing the right environment and the appropriate tool(s). While this study was carried out with language teachers, many of the findings are applicable to other subject areas where growing emphasis is placed on the development of collaborative skills.