In school we were all “equal”. As pupils, part of mass education program, we had no formal way to organise ourselves into preference based groups. But we did it anyway. I can bet that cool kids formed a very tight band in your school, one where admission was invitation only. You may have been part of one but the majority was excluded from the cool kids club and chose to join geekier ones. 

The behaviour does not change after school. Unlike schools, workplaces have very deep formal hierarchies. But the tendency to group ourselves into affinity-driven informal groups remains. In any corporation there are unofficial crowds where decisions are being made. It’s what people mean when they complain that there is too much politics in a company or that decisions are not transparent enough.