This study is part of a much larger research programme1 to reform teacher training in France. The specific aim of this study was to examine professional development of a preservice teacher in order to improve the organization and contents of this reform. The notion of professional development is currently undergoing a renewal of interest in the field of adult training (Borko 2004; Marcel 2009) for two likely reasons: training quality needs to improve to meet the expectations of the educational system and greater insight into how teachers learn to teach will enhance training programmes. In the broader research program, professional development is defined in relation to the processes by which preservice teachers learn professional actions. This entails identifying how they construct actions for thinking about their teaching activity and for acting efficiently in the classroom, as they interact with others. From this perspective, professional development is conceived as processes of internalisation (Matusov 1998) and social and cultural mediation (Bruner 1991) that contribute to transforming professional activity.