My first complaint is that many parents feel that supporting the teacher means telling them how to do their job. Parents....please don't do this. Why? Here are some reasons.
The teacher is the one in the classroom everyday, not the parent. S/he is the one who knows what's going on in that classroom. There is a classroom dynamic that many parents do not understand. They see their individual child. The teacher also sees that individual child, but additionally sees that child as part of a group. The entire group has to function well and the teacher is in charge of that. Only a person in the classroom can apply teaching strategies that will work for the group and the individual child. Those teaching strategies can vary from class to class depending on the students. Even in the same subject area, a technique that works in one class may not work in another.
Parents often make unreasonable requests of the teacher, again trying to tell the teacher how to do his or her job. I had several parents request progress reports be sent home on a regular basis. Usually, that's not a problem, but some parents wanted reports everyday. I understand that they wanted to keep on top of their child's work, making sure all assignments were done, but again, they were thinking only of their child. I was often responsible for teaching 150 students. It is almost impossible to meet this parent request.
Another bad situation is when the parent wants the teacher to allow exceptions for their child. I know that every child is different, but when there are classroom rules and deadlines for assignments, every student in the class should be expected to abide by those. If my rules had been unreasonable, I could understand, but they weren't. There were parents who asked if their child could only do half of each assignment. There were parents who asked that their child not be held to any deadlines. There was one mother who wanted me to tutor her daughter one-on-one after school every day. That was fine until other students started coming in after school wanting the same treatment. I did what I could, but on a couple of occasions the daughter had to wait for me to help other students. It wasn't long before the mother had the daughter pulled from my class and placed with another teacher. It's not that I cared so much that the daughter was no longer in my class (actually, it was a relief), but I thought this sent a horrible message to the daughter.
Parents sometimes forget that teaching is a profession. Teachers have taken many classes in psychology and teaching methods and should be considered to be the experts in this field. To me, telling a teacher how to do their job, is like telling a surgeon how to perform an operation. I'm guessing these parents probably do that, too.