I have worked with teachers (Primary) from 'the old school' who believed it was not only O.K. but effective to call a child naughty and stupid, to humiliate them in front of the class etc. in order to instill discipline & respect.
Whilst these teachers may have had a quiet classroom they also had children who had extremely low self esteem and who failed to reach their potential. I saw many a child wilt in assembly in front of their peers. But I remember seeing the same teachers being hugged at playtimes and being spoken of fondly by children & parents on leaving day.

Often, well aware of the methods used, parents seemed to appreciate that in this day & age it was refreshing that the child was not allowed to answer back, threaten a lawsuit or use physical abuse.
To label a child can cause such damage and feel that when a child is made to feel confident and learning is made exciting then their school experience should be positive.
However, I also have many friends (excellent, inspirational teachers) who have left their profession because of stress not only from additional, unnecessary paperwork but from the lack of respect by parents.
I believe what this teacher did was inappropriate behaviour for today but some of the responses as how to deal with it have saddened me. The first response should be to question the child fully. Yes, listen to your child but be realistic and have an open mind. Then make an appointment with the class teacher to express dissatisfaction. If not happy, then take matters further to the Headteacher.
I was once verbally attacked by a parent because her child had not been given clear enough instructions for her homework. The said homework was simply a suggestion I had made to the child's friend at playtime that perhaps if they had time they could draw me a picture of the school pond as she loved watching the fish!
It becomes a struggle to remain motivated when you do something which you believe to be in the child's interests and yet there is no respect or faith from the parents.
As has been said often, we do not know the motives behind the teachers actions. But when parents show teachers a lack of respect, then the children will also. Follow the correct procedure, do not lower yourself by being abusive. Only the children will suffer as more good teachers will leave and the classroom will become a place of tit for tat and not of learning & exploring.
Sorry to drag but the children are asleep & I have far too much time on my hands