Recent studies on virtual teams reveal that team virtuality may be considered from different levels which have a considerable impact on team processes and management. However, as a recent concept introduced to virtual team literature, virtuality and its effects on team effectiveness are still under studied. The purpose of this paper is twofold. On the one hand, it aims to define the concept of virtuality and provide a multidimensional approach to assess its different levels based on the main characteristics of virtual teams expressed in the literature. On the other hand, it analyzes how variations in virtuality influence team effectiveness. The effectiveness measures retained in this study are: work performance, attitudes and behaviours. A longitudinal qualitative study was conducted on ten virtual teams composed of three to five students involved in online Master degree programmes at a French university. The results highlighted the importance of differentiating technological and social virtuality to improve our understanding of team virtuality and to better apprehend its effects on team effectiveness.