Ferd in his signature school girl uniform, doing his magic on the guitar.

Their are two sides to this idea of dressing as a schoolgirl:
A. Floyd suggested it as a parody on Angus Young because Ferd is a crossdresser.
B. To prove you dont have to be all manly and macho to be a heavy metal guitar virtuoso, you can be gay, girlie and a transvestite too.
Basically to shove it up the stereotypes' ass.