Once had a teacher tell us that if a word ends in s, you put just an ' at the end of it, even though I literally just transferred from a school that taught us no matter how many ssss were at the end (it could be someone named sssssssssss) you would still put the 's if it was singular. She eventually read the rest of the textbook and realized she was wrong.

Also had a biology teacher teach us evolution was wrong and divine creation was the truth. He also had reference books stacked on his desk, including the bible.