Looking for a particular late 80s/early 90s female teen comedy

It played on Comedy Central in the mid 1990s. Featured a brunette girl and her blond sister (or stepsister) as they are sent to a boarding school. The brunette is wild and a prankster while the blond is stuck up. The brunette falls in love with a boy who goes to a rival school or is a janitor, something like that. There's a memorable scene where the brunette pretends to be visibly pregnant to shock the parents at a graduation. Anyone remember this?