This paper presents a model of professional development through the participation in a virtual CoP. This model is rooted in a definition of professional development and of professional practice. The model is then used for analyzing the activity of a virtual CoP of tutors involved in a computersupported collaborative learning training. The analysis provides guidelines for developing online services for supporting the activity of the CoP within a participatory design view. This research is part of a European project aiming at providing interoperable services for CoPs.