Out of curiosity, do you have a plan for the Teacher you find? Perhaps have him be infected and turn into a mini-boss, or just see him in the background doing something (fighting, sexing, both, etc.) Maybe he escapes and you meet him later? Just a little "Hey, I remember that guy!" sort of thing.
It would also be cool to find/rescue other survivors. We've already seen like 6 non-infected humans as background in the school. Perhaps a way to save them, or another interactable NPC then just the teacher? I'm assuming that you plan to have the next section of the game be out of the school and into the sewers, but having 1 more interactable NPC in the school would be neat.
Lastly, just going back on tabletape's comment. I agree with everything on it.