During three slots of two hours the participants were invited to discover and apply a model to analyse mathematical arguments in a classroom session where a problem is submitted to students. This model is based on different dimensions: conditions in which students elaborate reasoning when they solve in a situation, functions of reasoning (justify explain, argument, prove, demonstrate, etc.) and the syntactic and semantic dimensions. The model has been applied in three different contexts: the teaching of numeric functions at the beginning of secondary school, the numbers in primary school and the Archimedean tilings in secondary school.