It bothers me when students are taught "facts" that are just plain wrong. It's hard enough deciding what kids should be taught about controversial subjects in classes about history, social studies, culture, etc., but I think it's inexcusable for them to be mistaught facts that should be common knowledge. Being a school volunteer, I've often heard lessons in progress and have repeatedly noticed these mistakes. Sometimes it's carelessness by teachers. Sometimes teachers don't know the facts themselves. And sometimes there are mistakes in schoolbooks. Here is one exampe of each case, from my personal experiences: 1. An elementary school teacher had students copy a list of spelling words off the whiteboard. The teacher had misspelt one of them on the board, and all the kids copied it down that way, took it home, and studied it for a week. I didn't learn what happened when they took their test the next week, but I wonder if they managed to "unlearn" it later. This particular teacher did this more than once. 2. Another elementary school teacher taught the class that 0 divided by 0 is 0. When I heard about it from a student, I talked to her about it. She told me she is right, that 0/0 is always 0. I tried to correct her, saying that 0/0 is undefined, or at least indeterminate (you can make cases for 0/0 having various values using various mathematical approaches), but she simply didn't believe me. I also couldn't talk her into not mentioning 0/0 at all. She continued to teach it that way. 3. This week, I helped a class of middle school math students, and discovered that their school-issue workbooks gave them a list of prime numbers to factor, including the number 1. Primes are "positive integers that have exactly two factors" and 1 does not have exactly two factors, so 1 is not prime. This isn't controversial; it's just a definition. Yet these students will learn that 1 is prime from their books. I alerted the teacher, who agreed with me and will explain the mistake to the students. I don't intend this thread to be about math; that just happens to be the type of mistake I'm most likely to notice. My point is that it's a shame when students are taught the wrong information about basics like spelling and math, and I find it disappointing. Have you, as students, teachers, parents, or other observers seen the same thing? How often does it happen?