Silly Doubt = In or At?

[doltcrow]

I am ashamed because I have such a silly doubt and nobody could ever explain me the answer.
Well, what is the different between AT and IN, when it comes to refer to places?

For example:
I STUDY AT THE INTERNATIONAL LANGUAGE INSTITUTE
or
I STUDY IN THE INTERNATIONAL LANGUAGE INSTITUTE

Which one is right?
I mean, should I use AT when the place is speciefied and IN when it is not (park, work, school).
Or is it the opposite?

Thanx

 

[Francois]

You study in the USA/Japan/UK (country)
You study at UCLA/the Boston Institute/the MIT (specific place)
You study in law/science/accounting (major)

FRC