The Academy has more than just one school.
There is a school of gifted ghosts and ghouls, vampires and scrubuss, Werewolves and Undead students in their respected area of higher learning.
Millie is learning and is in a stage of mid level training.
Ghast has little things to do except trying to figure out how to get back home so he is force to do the tests while the board of directors have been watching his every move.
Believe me i've been planing this from the start ever since bleed finished making this little concept art for me