In this article we analyse a didactical situation centred on the creation and use of a symbolic play environment in a class of pupils aged five and six years-old. The main source of data for this paper comes from an experimentation planned in relation to the following research question: does symbolic play in simulated contexts help pupils to increase their mathematical activity in preschool learning? We draw on the sociocultural teaching and learning theories inspired by Vygostsky. We argue that the creation of and participation in a simulated context in classroom play is an adequate starting point for working on situations of social interaction and for promoting a joint construction of mathematical knowledge. The findings show the evolution of the pupils' actions during the symbolic game and the progressive incorporation of concrete arithmetical contents into their mathematical thinking. (Contains 4 tables and 4 figures.)