This paper presents a categorization of PCK that we have specifically developed to study the impact of a teachers training program (TP) on teachers’ practices. We present both our theoretical and methodological frame, based on the concept of PCK (Shulman, 1986) and the activity theory as developed by Engeström (2001) and some first results. The TP was videotaped and transcribed. PCK episodes were selected in the transcription and coded according to keywords derived from our theoretical framework. A cluster analysis based on the Multiple Correspondence Analysis of these keywords shows that two categories of PCK are at stake in the TP: what we have identified as specific PCK vs. general PCK. We show that this categorization is heuristic and allows some assumptions about the effects of the TP on teachers’ practices.