This contribution is based on research exploring the construction of lexical competence. Our didactic thinking has been built on lexicological theories considering the syntagmatic dimension in lexical analysis (e.g. Mel’čuk, 2004a, 2004b; Polpeu, 2008; Victorri, 1997, 2007; Picoche, 1986, 1993, 1999). We assume that an explicit study of the role of cotext in the interpretation of lexies can promote the development of lexical competence. The protocol put in place makes it possible to confine the cotext to frequent intraphrastic cooccurrents and then select a body of lexical units for which we analyse the field of the cotextual variation. On the basis of this analysis, we propose, for educational purposes, a simple grammatical structuring of the cotext. A didactic system comparing two classes of 6th (secondary 1) is then put in place in order to assess the impact of studying the structure of the cotext on the development of lexical competence. The two classes have the same teacher and follow the same path, with the exception of control over the explicit written teaching of the cotextual organisation of the lexical units studied, which takes place in only one class. Analysis of the data from the tests carried out at the beginning, in the middle and at the end of the journey shows that teaching the structure of the cotext allows students to develop a new approach to interpreting poorly known lexies. A subsequent test carried out at the end of one year confirms this interpretation and suggests that the study of the role and structure of the cotext leads to teaching sensitive to the syntagmatic dimension of the lexicon, which encourages the development of the lexical competence of subjects.