Generally speaking, the teaching-learning of French as a foreign language in the national education system often raises a whole series of difficulties. For this reason, the present study aims essentially to focus on a major and recurrent problem in the written productions of Moroccan secondary school students (college and qualifying). Our aim in this study is to study the vocabularies of secondary school and college students and to shed more light on lexical error, to find its origins in their written productions and finally to propose didactic and pedagogical approaches that can remedy this deficiency. The lexicon has always been, and unfortunately remains, considered the poor relation in the teaching and learning of French. In this sense, in addition to its marginalized place in the contents and programmes of the French language in secondary education, in recent years there have not been many issues and articles devoted to the teaching of the lexicon and vocabulary in journals on the didactics of French.