Teacher : inappropriate?

There is a boy in my child's class who is particularly badly behaved. He purposefully physically hurts other children and is quite problematic. He has been like this since he started school, he is now 7 years old.

However, today in class his teacher asked the whole cclass if anybody likes him. Nobody put their hands up. She then asked the boy how he felt about that and he said that he is sad that nobody likes him. My daughter thinks that the teacher did that so that the boy could understand that if he hits people he won't have any friends.

I am very concerned about the teacher's method. Maybe it's a last resort because they have tried everything else with him. What do you think? I need opinions because I don't know if I should tell his Mother what happened. I have spoken to her a couple of times and I am almost positive that she will complain to the school. But is it the shock the boy needs to improve his behaviour?