The spectacular increase in the number of non-native speakers among students, and in particular unaccompanied minors, in vocational high schools in recent years raises questions about the type of assistance that should be provided to meet their needs in terms of mastery of the French language. Starting from the observation that the lexicon occupies a central place in teachers’ practices and priorities as it represents a considerable challenge for students, this thesis addresses the question of vocabulary learning/teaching and presents and analyses the mechanisms that encourage memorization. In particular, the aim is to determine whether certain metacognitive and metalinguistic lexicon-related activities can enable non-native speakers, and more particularly unaccompanied minors, to become more independent and autonomous in their learning process.