Based on

Movies like Scooby-Doo and the Ghoul School (1988)

Scooby, Shaggy and Scrappy are on their way to Miss Grimwood's Finishing School for Girls, where they've been hired as gym teachers. Once there, however, they find that not only is it actually an all-girl school of famous monsters' daughters but there's a villainess out to enslave the girls.