Defined in a research about the Specialized Knowledge that is mobilized through video analysis and the discussion in a collaborative environment, we have selected the define and classify practices like a start point to reflect about the Knowledge of Practices in Mathematics (KPM) in prospective teachers (PT). In this paper, we show the results obtained through the content analysis of the individual reports and of the transcription of the group discussion. Our aim is to characterize the knowledge of practices in mathematics of PT, framed in the MTSK model. We found evidences of knowledge that allows us to reflect about the relationships that prospective teachers do between define and classify practices that can be useful to construct materials for their education.