1999 film by Helmut Dietl

Eleven-year-old outsider Stephan arrives at Castle Schreckenstein, an all-boys boarding school, where he learns about life within a community and soon finds himself being part of a funny 'pranks-competition' the boys are currently fighting against the neighboring girls of Castle Rosenfels. When the girls have no choice but to move to Schreckenstein after a failed prank, life at school is suddenly nothing like it used to be...