I walked into a 5th grade math class once. The teacher was saying, "You never, ever, ever divide a large number into a small one!" OK. Maybe this is why we have so much trouble teaching math in middle and high school.
We had a huge blow up my 2nd year teaching. All the teachers invovled were either 3rd year or 2nd year teaching (so we didn't have a much supplemental materials of our own). The 5th grade teachers were having trouble with a concept in Fractions. The kids swore up and down they had never been introduced to the concept, but the book taught it like it had been introduced.
I went back to the curriculum and realized while book started the concept in 4th grade the state standards didn't start it till 5th. So the 4th grade teachers going by the curriculum had skipped that chapter.
I went to the other 5th grade teacher and showed her this. So problem solved. We could just ask the 4th grade teachers if we could borrow a few books and get copies of the blackline masters. The supplement with some stuff I had found and we could teach the concept. I would talk to the team leader the next day, because I was leaving right after the kids did to go to the doctor.
The next morning I walked into a hornets nest. Some busy body had over heard the other 5th grade teacher and I talking. She had gone with a twisted version that we had said they weren't teaching math to the 4th grade teachers.
Adding to the tensions the other 5th grade teacher and I had traditional licences. All but one of the 4th grade teachers were alternative certification canadiates/licenced. (I didn't know it at the time but the principal back then was treating alternative certification people very badly.)
The 4th grade teachers were angry. I managed to get them to listen to what I had actually said - that they weren't supposed to teach concept - but the book assumed they did so we just wanted to borrow the 4th grade materials on concept.
The tone changed very quickly and we actually went over the rest of the curriculum exchanging materials that the curriculum put in different grades. I brought up the whole telling kids we don't do X, when X is actually taught later in the curriculum. Now we say things like "In 2nd grade we don't subtract big numbers from little numbers. Or in 4th grade we don't put big numbers over littler numbers in fractions" The kids know that means they will do it in upper grades at some point.