This study focuses on identifying values, specifically conceptions and attitudes towards sustainable development (SD) and implementation of Agenda 21 in a school. Data were collected from a questionnaire. Responses of 80 students and 22 staff members at an agricultural school were analysed. Students' responses highlighted the centrality of the environmental dimension of SD. The difference between staff's and students' conceptions of SD related to the categories of " responsibility " and " awareness ". Related activities within school, students and staff mentioned a very limited number of actions, essentially " eco-friendly gestures ". These actions are necessary but not sufficient to achieve sustainable development, and may constitute a basis for more complex actions. The factors referred to as hindering commitment to SD were both institutional and psycho-social in nature. SD redefines the boundaries between the academic subject approach/a-disciplinarity (or the cross-curriculum approach), teacher/person who educates, class/school/local surrounding territory, knowledge/values, acting/thinking. These boundaries change the modes of action and the organisation of the teaching-learning activity by introducing new players, values and relationships.