In this paper, we present the results of a study on the circumstances in which instructions given by various interlocutors (cooperating teacher, university supervisor, colleagues) favor the development of professional activity of a preservice teacher. The study was conducted within the framework of the Cultural Historical Activity Theory (CHAT) (Vygotsky 1978, 1997) and activity theory (Leontyev 1981), with its methods for the clinical study of activity (Clot 2008). The results show that the preservice teacher's intrapsychic conflicts arose from the concurrence of and discordances between the instructions stated by the various interlocutors ("inter-psychic conflicts") and from the confrontation between these instructions and the experience of classroom. These conflicts prompted the development of the preservice teacher's professional activity through the construction of new goals and new motives for action (development through sense) and the construction of new operations to reach these goals (development through efficiency). This study suggest that collaboration between a cooperating teacher, other teachers, and the university supervisor in a school setting provides the conditions for encouraging and guiding the professional development of preservice teachers.
