Abstract : This thesis aims to highlight mobilization process of students for vocational training curriculum and its relations with development of activity goals and training situations characteristics. We adopt an ethnographical approach to follow thirty nine students enrolled in a vocational training to become food industry technicians. We use the theory of activity developed by Rubinstein (2007) as supportive framework, in order to distance ourselves from "motivation" psychological approaches. We develop the concept of mobilization process, initially proposed by Charlot, Bautier and Rochex (1992). Our analysis consists in : * a description of the three curriculum and their training situations ; * a statistical approach of mobilization conditions of students for different training situations ; * four students' monographs. Our results show that mobilization condition of students for a specific situation depends on situations of their past, present and project life. But characteristics of current training situation update this mobilization conditions. Some of those characteristics are very important in the mobilization process: coherence between aims of the situations and professional aims of the curriculum ; knowledges that are presented as tools for professional situations ; creative tasks ;...Students are mobilized for situations where actions allow them to realize, build up and show their personality. Those situations found long lasting goals for their activity and establish continuity in their "whole life itinerary". This does not improve their student performances. They are demobilized when situation parceled out their activity, which couldn't coordinate any more actions with goals of activity, personality characteristics and tasks conditions. Their student performances decrease in that case. In conclusion, we propose some developments for the Rubinstein's theory of activity and for the theoretical framework of professional didactics. We suggest lines of enquiry for professional training, vocational guidance and school dropout.