The most harmful type of bias relevant to education is Fairness Bias. Teachers and parents tend to think each student in the class should get the same amount of attention from the teacher as any other student in the same class. However, this is not true. Each student in the class has different intelligences and learn in different ways. For some students, certain topics are easier than for other students. It may not seem fair that the teacher works one-on-one with a one child while the rest of the class is doing the classwork the teacher gave them. That child might be far behind the rest of the class or really struggling to grasp the topic whereas the rest of the class is doing fine and are getting farther and farther ahead of that one student. Now how fair is the extra attention? Or, maybe that child is more of a visual learner as opposed to a bodily-kinesthetic learner. If most of the class is bodily-kinesthetic learners (which a lot of people are to at least some degree), then the teacher is trying to help that one child out by reteaching the lesson for them in regards to their learning intelligence so the child understands the lesson better, is that really unfair?
Any one of these situations could cause problems to arise with parents. Then, there is a possibility the parents will try to get other parents on their side (which could be through the media). However, the teacher is just trying to do their job and make sure each of their students are keeping up and understanding their lessons. If any of these situations goes to the media, it could affect the teacher’s ability to teach. For one (and this is a long shot) the school board could temporarily suspend the teacher until the situation blows over or is resolved. Then a sub would have to come in and how well are the students going to learn then? It could also be hard for the teacher to teach because parents could be second guessing them, causing their lessons to take longer. The teacher might also have to spend more time (outside of school periods) talking with parents to appease them and ease their minds.
Either way, both the teacher and students suffer so it is a lose-lose situation for all involved. The parents may be aiming to help their child, but in reality, they are hurting their child. Think about how hard it would be to do your job with someone constantly breathing down your neck, second guessing your decisions, possibly interrupting your lessons.