What is the scooby Doo movie that shaggy scrappy and go to an all girl monster school?

The Scooby-Doo movie where Shaggy, Scrappy, and Scooby go to an all-girl monster school is Scooby-Doo on Zombie Island.

While the movie doesn't feature an all-girl monster school, it does have a school for monsters called "Monster High", where Shaggy, Scrappy, and Scooby investigate strange occurrences.