This paper presents a Vygotskian research device that focuses on collaborative activities based on the manipulation of linguistic objects in a primary school classroom, with 8-9-year-old children. Through social exchanges among the different points of view, the children were engaged in a dynamic process of building and negotiating mathematical meanings. How the children may become aware of the possibility that the same language can have different interpretations as well as some aspects of the distinction between syntax and semantic is analyzed. The analyzed activity is the "worlds' game," the final step of a didactic path based on the construction and manipulation of a procedural language. The content analysis of the elicitation interviews allows to reconstruct children's reasoning, individually developed during and after the activities. From a qualitative analysis, it emerges how almost all the children reached a good level of awareness and mastery about the possibility that the same language can have different interpretations and, therefore, about some aspects of the difference between syntax and semantics.