Contrary to belief, the presence of boarding facilities, and thus of supervisors or study masters, attached to an Ancien Régime “collège d’humanités” (grammar schools teaching the classics), is far from systematic. Even if cases can be identified as early as in the 16th century, the practice only becomes general towards the end of the 17th century. The men in charge of the boarders when out of the classroom go by different names all along the modern period, according to the type of school they are attached to: “préfet de chambre” – dormitory prefect, “préfet de pension” – “board prefect”, etc. But beneath these names there is always the same character, defined by two permanent traits: on the one hand he never has the title of professor or of regent, but, on the other hand, he is invariably in charge of two tasks which are nonetheless of a different nature: the organisation of pedagogical activities during study time and disciplinary supervision during the day. This paper will study the reasons for and the modalities of the combination of these tasks. It will also turn to another central question: does this practice constitute a sort of preparation for a future teaching profession, compensating in a way for the absence of professional teacher training for professors through the exercise of pedagogical skills in a minor key (at study time) ?