The topic of this article is the study of collective activity during practical work in a vocational school. Its purpose, in focusing on “activity”, is to describe the different types of interactions that occur between pupils and teacher in order to identify their role in maintaining the efficacy of the activity and of the learning processes. Reconstructing the organisation and meaning of the activity has brought to light typical ways in which collective activity gets structured, which organise pupils’ longterm investment in the activity and open up learning opportunities. Close analysis of an exemplary case showing the process of coordination and adjustment demonstrates the way in which teachers exploit the emergence of production mistakes, in order to incite the students to build new knowledge that can be put into practice during production processes, and in order to enlarge their understanding of their theoretical knowledge. The article discusses the link between the way activity is structured and a shared culture, the relationship between production activities and building activities, and the specificities of the dispositions of teachers engaging in the transmission of practical work.