Beauxbatons has a unique sorting method. In order to be sorted, you must shoot a silver arrow across the room. After several seconds, the arrow will burst into sparks of your house color: Purple for Papillionlisse, Blue for OmbreLune and green for Bellefeuille. The arrow will choose a house based on your personality, character, and demeanor. Certain traits exemplify certain houses. You may possess all the traits or strongly possess only one of them. The house descriptions are outlines for your character, but not definite facts.
Source: http://beauxbatons-academy-of-magic-roleplay.wikia.com/