Plot hole: The whole point of the deception is that Fern Mayo, the geek, turns overnight into Vylett. No one at school has a clue about her real identity till Marcia and Courtney put up posters. So this deception carries on for several weeks before the two girls expose it. There is no way this would work. A school will not simply accept a new student without bothering to register her, yet when Fern Mayo just doesn't turn up to school one day, and Vylett does indeed, none of the teachers find this strange, or bother enrolling "Vylett" officially in school.