There is no actual level or area in the game called "Evil School". The phrase is a nickname for the Cortex Compound, the main hub and the central villain's headquarters in the game.
Here's why it's called Evil School:
* The Location: The Cortex Compound has classrooms and a giant clock tower, visually resembling a school.
* The Tone: The game's story revolves around Cortex brainwashing students, and the atmosphere in the Cortex Compound reflects this villainous purpose.
* The Gameplay: You'll be facing a lot of mutated students and teachers, and the entire experience feels like navigating a dangerous, sinister school.
So, while there's no specific "Evil School" level, the Cortex Compound itself is essentially the evil version of a school in the game.