There was always some element of indoctrination involved.
I grew up in a purple-red area politically, and remember in elementary school learning all about the O-Zone layer,
saving the whales, stopping deforestation, Earth Day, and all that sort of stuff, from a strong pro-environmentalism perspective, bordering on hippie-ism. They unironically showed us the
"Rainforest Rap" that says "by the year 2000 [the rainforest] will all disappear...", in the year 2000.
Later on, in high school, I recall reading "The Invisible Knapsack" (about white privilege) at some point. In AP Literature, we were made to read Upton Sinclair's socialist work "The Jungle" and the feminist classic "A Handmaid's Tale". I took a sociology elective, since it was one of the only options I had in that time-slot, and that class was nothing but indoctrination. However, it was taught in such a simplistic way (the textbook was at a 7th-grade level, and the class was mostly vocabulary word searches) that the indoctrination was near-worthless. Still got to learn about how all the Social Justice stuff ties into critical theory and Marxism, though, since this was years before discussion of that topic was highly politicized and verboten.
Regardless, I'm not sure we were ever really asked to engage seriously with anything right-of-center. Except by my economics teacher, who liked to show us John Stossel videos in class sometimes. Also, in the 8th grade, state standards required that they teach us about Islam, its tenets, and how it is a "religion of peace". My highly conservative social studies teacher did so reluctantly, and as a counter-point, would read Bill O'Reilly For Kids to us at the end of each class period.
Overall, things weren't as overtly political in class back in the day, but teachers were still more progressive than the average, and that did work its way into their lessons sometimes. As a side note, I recall several classes (typically social studies, or oddly enough, health class) actually having political discussions that were civil on both sides, something that I don't think would be likely in today's environment. It was just a different time.