This is a somewhat silly and erroneous movie. It's about rebellious french schoolboys fighting their teachers and taking over. The plotline devolves mostly into antics conducted by these boys in order to create a full state of anarchy. The film is interesting in that it rebels against the social conventions of the times by almost encouraging this sort of behavior. I would argue the film is dangerous in the way that it succeeds in putting you in an anarchic chaos based mindset. There's no rhyme or reason for these children to misbehave apart from the fact that it's something different. I will take issue with this rebellious for the sake of being rebellious attitude of French Filmmakers in the French New Wave which this film is absolutely a forefather of. Truffaut, Godard and other radical filmmakers of the 1960's would borrow from this film as an example of anarchy onscreen depicting schoolchildren (the ultimate prisoners in their mind) rebelling against the prison.
I found this movie kind of objectionable because there was no good explanation for why these boys were behaving like this and no chastisement of them for behaving like this without any good reason except that they were bored. This is a self-destructive cultural mentality that I will grow to dislike as it gains traction in the 1960's.