My high school civics teacher was, I kid you not, an avowed Marxist who had a big "revolutionary" banner (in Russian, with a big hammer and sickle, an image of Lenin's head on it, etc.) hung up on the wall so that if you were going to look up at the blackboard for any reason, it would always be in your peripheral vision. He also had a small bust of Lenin kept away in a closet, and would take it out and have students rub Lenin's head for good luck on test days. This stuff wasn't up for a unit on communism or the cold war. It was up year around, along with those annoying bumperstickers with sayings like "A woman who seeks to be equal to a man lacks ambition" or "A woman needs a man like a fish needs a bicycle" on them.
He retired about a decade ago in good standing after about 30 years on the job, with full benefits.
I don't agree that the walls of the classroom in a public school are or ought to be vehicles for the expression of the instructor's views, but I also haven't ever seen teachers like the one I had (who I actually liked quite a bit as a person and a teacher, but his ideological bias was hard to miss) ordered to tone down the expression of their own views. I wonder what the FFRF would think about my high school civics class.