Hmm.. I was thinking that they could be eternally stuck there in that grade maybe?
Or perhaps they graduate once the creator of that character is tired of them and makes a new character.
Here is another question maybe someone could answer:
Is PCA opened as a year round school with vacations every so often?
I think that would be cool, say some students go on vacation while others could choose to stay.
This could add drama. Maybe as a plot later on..