Good question. Bus stops are small - you can't get into them, so at a bus stop, at the bus stop. . I attend university = I am at university. Where are you? I am on the university campus right now = I am at the university. What do you do for a job? I am at the university. . If the bus stop is a big building, you can be in it. Not a common thing to say. I am at the train station = I am there. I am in the train station = I am there, on the inside. . He excelled.in school - during those years She excelled.in university - during those years She excelled at school He excelled at university.

I would have to say neither. For the first one I would say, "I am at a bus stop." For the second one it depends. If you were literally inside the university, you could say "I was in a university."　Though you could say this one whether you were inside (which is still at a university) a university or around the place: "I was at a university." If you wanted to mention that you were taking classes at a certain university, you could say "I took college classes at a university." Or something like that.

Agree with naren....!!!!