This paper presents a study of behavioural variables implied in the working dynamics of student groups undertaking their first project. The study was carried out in two phases. During the first phase, the participants answered a survey of open questions regarding their own behaviour and that of their teammates, questions related to: the quality of their work as a team; their individual contribution to teamwork; and their perception of what they learned after taking part in the experience. Analysis of the answers through the inter-judge consensus method has been the basis for developing a questionnaire of closed questions, which has constituted the second phase of the study. The procedure followed for developing the questionnaire and the results obtained after handing it to 92 students guarantee its validity and reliability for measuring and assessing the behavioural variables implied in how such groups work. The study concludes with the prospects for using such a tool, in order to support the work of student groups throughout the course. (Contains 5 tables.)