Propaganda is conspicuous for what it conceals and always cautious about what it reveals. Starting from the assumption that all documentaries on the Decroly School in Uccle (Brussels), the school Ovide Decroly (1871-1932) founded in 1907, are propaganda, this article tackles the question as to how to "read" this particular set of Decrolyan propaganda documentaries. The author will do that on the basis of two documentaries--"Pour la vie, par la vie" (1946-1947) and "Le Jardin d'enfants a l'Ecole Decroly" (1952-1953)--and focus on what he calls a contextualising "from within": a filmic reading as part of a historical reading. What does the "genre" of the propaganda documentary, the way these films are constructed, reveal about the Decroly Method, the Decroly School and the Decrolyans? This implies that one needs to try to unravel the "grammar" or "semiotics" of the films. As a result, this article is starting with a methodological reflection on how to read (propaganda documentary) film, after which the author outlines briefly the production context of the Decroly films. The subsequent sections relate this context to a contextualisation "from within", focusing on the voice-over and the sounds, the framed images and the camera work, particularly related to the way space, children and adults are depicted, and finally the editing work, particularly referring to some striking sequences. (Contains 59 footnotes.)