The aim of this paper is to determine the way supervisor work while managing a joint evaluation performed at the end of a traineeship. More specifically, our research questions are the following: Do all the actors of one single schooling institute have the same concept of a joint evaluation in mind? What practices are common to the supervisor of a schooling institute, while managing a joint evaluation? What are the differences from one supervisor to another? How much does the individual’s concept of a joint evaluation influence the actions of a supervisor? In order to find answers to our research questions, we gathered two sets of data from eight supervisors of the same institute: we interviewed each supervisor during approximately one hour and taped, for each supervisor, two joint evaluation sessions. The analysis of the content of all the gathered data shows that the interviewed actors don’t all have the same goals with the joint evaluation and that they have distinct ways of managing the joint evaluation, based upon their concept of joint evaluation. Six variations were found, that are directly related to the dilemma accompanying/training vs evaluating/certifying. We have demonstrated here that, even during a formative traineeship, some supervisors have difficulties leaving the state of mind of an assessment.