There was actually a mini-course in critical thinking in my fifth- or sixth-grade class, I forget which (I spent two years with the same teacher and essentially the same classmates). It was the late seventies. There was a textbook and everything. They talked about reasoning from prejudice, emotionally loaded statements, various logical fallacies.

My understanding is that whenever people try this in primary or secondary education, it's politically unpopular because it's considered a stalking horse for liberal secularism.