We had a similar thing going on in reception. In the beginning of the school year a group of boys (the football players) formed, whereas the other boys each remained quite isolated initially. I think it was a bit of a status thing, the group that had bonded together was perceived by the others (certainly by my DS) to be desirable, he desperately wanted to belong. But some kids in the group, one in particular, used the ability to repeatedly reject/isolate/belittle my DS as a means to secure their own position in the group.
It was heartbreaking to watch and had devastating effects on my DS' social confidence. There were times when we did consider removing DS from the school. And if it hadn't improved pretty soon, we would have.
We did talk to the teacher who did keep more of an eye for a while, did some carpet time talks, and directed DS towards different kids for a while; but it all petered out again pretty soon. Teacher stated she thought the situation to be resolved when it was far from that.
We also did lots of work at home, mainly instructing DS to keep away from said boy, and practising ways to respond to certain situations. He eventually formed a new group and made some excellent friends.
That other boy still seeks out opportunities to reject and belittle my DS (and others), however my DS sees through it now, is confident with his own group of friends and it barely affects him anymore (in Y2 now).
In your friend's child's situation, it sounds to me as if the child needs to stop seeking acceptance and find/form a separate group of friends. If they are otherwise happy with the school, I'd say give it a go, talk to the teachers again, and work with the child at home.