From several sources the advantages of a methodology based on work in groups at university have been pronounced. It is desirable to have a method to assess not only the product but also the group process. Nevertheless, the university professors, perceive certain deficiencies and disinformation, especially with respect to the assessment of the group processes. For this reason, we try to respond to the following research questions: is possible to measure the process of the group even in large classrooms? Are the process and product marks correlated? Can be avoided the bloodsuckers? What problems arise? We have designed and proven a grill of observation and we have analysed an ample set of data. It seems evident that the proposed system successfully curbs opportunist behaviour patterns of students and that the main drawback, from the students' point of view, is that they are forced to put more effort into the subject.