The most overtly religious event I encountered in school was the Gideons handing out New Testament bibles in class when I was in fifth grade (around 1974). I still have it. Other than that incident, my public school experience was pretty cleanly secular. I never had a teacher try to proselytize, push creationism, or anything like that. I don't recall ever having a school led prayer. The nearest thing was the "moment of silence" that they had each morning at one of the Jr. High Schools that I went to. There was no compulsion to pray or anything else during that time, so it was pretty unobjectionable other than maybe being a waste of class time. It lasted about a minute. I'm not sure whether there were any religious plaques or banners in any of the schools I went to, as I don't think I would have noticed such things back then.
We hear about these kinds of incidents pretty often, and some of us have personally encountered them, and there may even be a few schools where it is a systemic problem rather than just isolated incidents or a lone rogue teacher. But I think that most U.S. public schools actually do a pretty good job of keeping church and state separate most of the time. Even in the right-leaning states where I went to school (Texas, Indiana, and Arizona).