Certainly they can't just wander freely inside and would be questioned, but even if said person is asked to show their ID the person doing the questioning likel

Certainly they can't just wander freely inside and would be questioned, but even if said person is asked to show their ID the person doing the questioning likely won't know offhand what the person's history is. However, there may be people on the outskirts of the school looking in. I know when I was in all levels of school there were fences and areas where anybody could just loiter and hang out, and not necessarily look particularly suspicious.