AN: From interactive "Fanfiction Gender Change", chapter originally written by Lonly Wanderer
''Any time 'Arry'' Fleur laughed and smacked him on the shoulder, unfortunately he was standing on the edge of the bath, and slipped falling into the water with a splash and a flash of light.
As Beauxbatons was an all girl school certain areas were warded to prevent boys from entering, usually dorms and bathrooms. In the case of the carriage the ward lines were in the doorway and around each individual bath itself. The doorway ward was similar to the Hogwarts girls dorms, designed to prevent males entering, usually in the form of the door becoming a wall. The ward around the baths were a more active prevention, ejecting the boy from the carriage and alerting the Headmistress.
Harry was unaffected by the initial ward (not that he'd have been able to do anything from in her bra) because he was too small for the wards to recognise as a male, or even a wizard so had no reason to activate. When he fell into the water he triggered the inner ward, this then interacted with his still unstable magic as it tried find a way to bypass the effects, coming up with fairly a permanent solution, or at least something that a Hogwarts student (even one as strong as Harry) can't reverse.
