
Fear inhibits learning. A child that is afraid of failing is less likely to try new things, and so their learning exposure is limited. They will engage less with the teacher and the class, again reducing learning opportunity. A child that is afraid of the teacher is also less liekly to approach them if they don't understand something, less likely to get excited about and interested in something they are covering in school and more likely to take step to not be afraid, such as skipping school. The fear may also cause them to panic in on the spot situations, among others, and more likely to make a mistake that they otherwise would not have done.
Fear, then, is a bad thing. Fear is also used to control children - punishment for deviance with reward for good bahaviour, as dictated by the teacher. We don't think that it is particularly appropriate to contol children in such ways. It's bullying, and no-one likes a bully. We thought, how about having a good relationship of mutual trust and respect? It's not a new concept but it can be challenging, as the teacher needs to be much more consistant. The teacher also has to be comfortable with a more friendly relationship with the children. Because of the inherent contradictions in mainstream education it doesn't work, the children see it as another reward/punishment scheme and so set about trying to pull it apart.