1. Principal
2. Teacher
3. School assistant
4. Fast food worker
5. Fast food "Relief Officer"
Your ending depends on your final grade. It's the combination of both tests and the group project. The better your score, the better your ending.
I don't know how you did it, but ending 5 is the most difficult to get. You'd need to have complete understanding of the game mechanics and do everything "wrong" on purpose.