The only flying mammal is a bat.
Not according to my Grade 4 teacher. I mentioned her before - when I said "bats" as an example of a mammal, she laughed at me and said "Bats aren't mammals!". Then she encouraged the entire class to laugh at me. Yes, I'm still a bit bitter!
My sister’s 4th grade teacher was convinced that Ben Franklin was a U.S. president. Even with my mom’s intervention, I don't think she ever got her grade corrected for that assignment. (IIRC, it was about presidents and our currency. I guess since Franklin and Hamilton are on bills, they clearly
must have been presidents or something)
Another thing that made my brain hurt: in high school, I spent one year at a different school and since I was a new student in the district who enrolled a week into the year, they put me in the only history class for my grade with an open spot. It was… I don’t want to say remedial, but certainly not even honors level, let alone the AP class I would have been in at my other school. Without much effort since the coursework was simplistic and there was a lot of available extra credit, I generally had about a 110% in the class. Being the full-of-myself kid I was, I stopped caring at some point and just didn’t do an assignment. Instead of lowering my grade or disciplining me in any way, the teacher gave me full credit anyhow. She was also convinced that Pres. Buchanan was pronounced "Buck-nan"… and her specialty really was (supposedly) American History.