satopi
Life doesn’t end, …it changes.
Most schools wouldn't let Ash carry an animal in class unless it was a service animal.
But in Alola, they live peacefully along with Pokémon so it could be their study partner/buddy/assistant. Maybe the teacher is chill. I want to see what's in Ash's backpack. We've barely seen what was in it.
Edit: Lillie's hat would be a big sitraction and poor Mallow wouldn't be able to see what's on the chalkboard.