The word “dispositif” – the organisational format set up to meet a specific goal, usually a policy goal - is currently in very frequent use within the school environment. It can be found in official and institutional texts, but also in any number of research papers concerning schools or similar institutions. Yet, in most cases, the word is used without great precision or reflexion as to its meaning. This paper will therefore focus on the word and try to define its uses, with the hypothesis that its semantic extension is a way of better accounting for present-day school realities. We will first show how the word, while remaining faithful to a specific analysis of a school as a set of instruments and infrastructure, has come to designate some of these among others, thus modifying the traditional format for school organisation. We will then show the strategic functions of the instruments and infrastructure thus picked out, as they reveal and to a large degree account for the hesitations which presently characterise the institution, regarding both its objectives and its means of action.