An old musician, mr Mathieu, arrives to a boarding school for ill-mannered young boys, called Fond de l'Etang, in France. The school's motto is "action - reaction" (pretty much "if you do something bad, be afraid"), which clearly isn't working, since all rascals are behaving like tiny (and big) monsters anyway. Mathieu finds the school's motto to be wrong and takes a whole new approach to the teaching methods, changing all the boys' lives forever, through singing. (Despite that, this is not a musical where everybody suddenly breaks into song at random times!)
( click for my thoughts on this! )