For me, it was mainly the philosophy and politics teachers. Boy oh fucking boy, for some reason, every single one of my philosopy and PolSci teachers were... interesting personalities to say the least. It was our philosophy teacher who introduced us to the Labor Theory of Value, oddly enough, and the issue of economic inequality. And as for the PolSci-Side, two teachers stand out: One grew up in the GDR and was very, very nostalgic about it (with some fair criticisms, especially concerning the Stasi), and the second, and final one in my case, was an irony-poisoned super-leftist with a gigantic disdain for the rich, the state and capitalism.
My senior year history teacher showed us the third Zeitgeist movie which was my first introduction into anti-capitalist thought.
Wow thats awesome.... this one definitely led me on the path. I was a right-libertarian when I watched this, and I think that movie is a pretty defining moment in my rethinking of things.