On the contrary, I don't think cliques are a problem at my school. I think my school has a very pleasant social environment -- much more than other schools I've seen. For instance, I visited my cousin's school and the social environment is very cliquey and snobby. If my observations don't provide enough evidence then my cousin's persistent complaints corroborate this opinion.
In my school there's basically just normal people and weird people, and I'm one of the weird people. The idea is to share our weirdness with normal people. Maybe infect them
EDIT:
The above was probably an abuse of sarcasm and humor. I'll be more clear and say that I'm very friendly with people outside my social group every day in school. We talk regularly, we work in groups, etc. But we never hang out together or instant message eachother. So we don't get to share our lives with eachother -- that's the crux of it.
In a sense, what I am saying that there are many people around you who have the potential to be your close friend but never ends up being one. This can be because you don't share a common interest intensely enough to immediately befriend eachother on that basis. Or because you never sat next to eachother in a class. All of these are trivial circumstances that should create neither boundaries nor barriers.