The presentation will be focused on the methodology of analysis of classroom productions (utterances and gestures of teacher and students). The chosen perspective is the knowledge involved in classroom practices. We consider that the taught knowledge is staged in the classroom by teacher and the students' joint action. Following Grice, we distinguish between conventional (taught knowledge) and understood meanings (students' or teacher's understanding). Here, we propose a methodology to analyse these types of knowledge: taught knowledge and knowledge understood by the students or the teacher at two time scales, the meso scale (about ten minutes) at which ideas are developed in the class, and the micro scale (about seconds), which is the scale of interactions between individuals (teacher and students). The collected data, which this methodology works out, consist of several hours of video recordings of physics and chemistry classrooms at 10th and 12th grades during teaching sequences on a specific part of the official curriculum (in physics and in chemistry). The meso scale analysis is based on a thematic approach. The discursive productions (including gestures) can be divided into units of about ten minutes. The micro scale analysis is based on a decomposition of knowledge into “facets”. Processing facets (without recomposing them to get a concept meaning for example) leads the researcher to characterize classroom according to the density and continuity of the taught knowledge. Treatments involving meso and micro levels allow the researcher to compare this taught knowledge to the meanings constructed by the students.