Students enrolled in vocational high schools (VHS) who have undergone an unchosen orientation, particularly in industrial fields, have difficulty engaging in school work (Arrighi & Gasquet, 2010). In this respect, the teacher-student relationship based on the teacher's social support appears to be a lever for their engagement in school work (Jennings & Greenberg, 2009; Poling et al., 2022). The aim of our research is to analyse this supportive relationship between the teacher and all the pupils in the class, based on an analysis of their activity and their experience in class, over the school year. The aim is to investigate the following questions: a) do students in difficult VHS classes experience support from their teacher during the year, helping them to engage in class work? b) what is supportive for them and allows them to modify their engagement? c) can we identify moments of support for work that are shared between the teacher and the students in the same class, and what is the dynamic of construction of the experience of support lived by each during these moments? To analyse the activity and experience of support in the classroom, we conducted our research in the Course of Action Research Programme (Theureau, 2006, 2015) in cognitive anthropology. Using a mixed method (Greene et al., 1989), we collected and articulated two types of data, at three periods of the year: quantitative data, collected from the CASSS questionnaire (Malecki & Elliott, 1999) presented to 304 students from 15 classes, from four VHSs; and qualitative data collected from a self-confrontation interview conducted with four teachers (n=19) and 18 students (n=35). The data processing consisted of a statistical analysis of the students' perception of the teacher's social support, and the identification of the components of the teacher's and students' course of action (Theureau, 2006). Second, the data were articulated to understand the construction of support for work engagement in the classroom over the course of a year. At the level of all students studied, our results show relative stability in the perception of a supportive teacher throughout the year for students. However, at the quartile level, perceived teacher support varies over the year. The situational updating of mutual knowledge between teacher and students appears to be the cornerstone of shared support moments. A local analysis of the moments of support experienced by the students allowed us to identify certain actions of the teacher (i.e. physical engagement, individual speaking, or his physical presence) as signifying for the students a help to get to work. Finally, our study defined, from the teacher's and students' perspective, teacher support as a compromise between "being demanding" and "caring". The results are discussed in four points: 1) students' perception of teacher support over the course of the year as an important dimension of LP students' engagement; 2) teacher support against a backdrop of humour and emotional security as a cornerstone of their engagement; 3) mutual knowledge at the heart of shared moments of support; and 4) the integration of the contextualised questionnaire with the PRCA observatory as a mixed method for accessing the experience of classroom support. Future methodological perspectives are then proposed to enrich this research.