The present study focuses on the actual practice of mathematical work by students and teachers. In order to investigate this question, a series of classroom sessions were developed for use in a teacher training course. The sessions were subjected to analysis using the Theory of Didactic Situations (TDS) and the Theory of Mathematical Working Spaces (ThMWS). The combination of these two theories has enabled the development and implementation of a coding system for the observed sessions. The coding facilitated the examination of the idoing (potential and actual) MWSs that emerged during the training. In particular, it permitted the identification of distinct patterns, which enabled the recognition and characterization of different forms of strongly didactic contracts. The tools, and in particular the coding, developed for the study could be employed in future research on didactic situations in relation to the idoing ETM.