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.
Good question. Throughout middle school & high school I had generally young, progressive teachers, and while that didn’t manifest itself very often, when it did I think it made an impact. In college, my polisci instructor was a liberal, a real kool aid drinking, liberal democracy worshipping type of liberal. Sometimes we’d have discussions about how broken the political system is and I radicalized a bit through my disagreements with him in that regard. My history instructor was a former veteran who served in central america and at some point woke up to how immoral American foreign adventures are. We used a Howard Zinn history book (paired with a conservative one for “balance” but it was clear which he preferred) in that class, which was utterly awesome.
Other than that, I’ve taken STEM courses and politics pop up only rarely.