When I was in high school, the cafeteria was the place to find out who was in who's clique. Seriously, you could walk into there at lunch time and immediately see a representation of every clique and who is in them just by who sits next to each other.
The most enthusiastic clique though? Those that played Magic: The Gathering, Pokemon and other similar card games.
Seriously, they were always gathered together and all paying attention to the same thing.
And they were congregating around one main common interest.