This study analyses the impact of the interactions between preservice teacher and all interlocutors of the mentoring situation on the development of his professional activity. This study supports on concepts inspired of cultural historical activity theory approach and clinic of activity approach applied to the work of education and training. Four types of data were collected: semi-directive interviews, video recording on activity in classroom of the preservice teachers, self-confrontations, ethnographic data. The analysis of data consisted in reconstruction the practical reasoning of three preservice teachers and of their interlocutors by the identification of rules enunciated in interactions. Results allow to identify: a) the development of the professional activity by meaning making and by effectiveness, alternated by purposes and motives of action and construction of new operations to act in classroom, b) the rules enunciated by the interlocutors of mentoring situation as means of the preservice teachers' professional activity, c) the circumstances in who these means contribute to the development of power to act preservice teachers. This study registers in actual debates relating to the professional training of the future teachers and to the conception of implements of training in link of the reality of teaching work. The study is also a tool for the professional development of the preservice teachers and of the training teachers
