You have my sympathies 
My DS has, in the last month ,been kicked to the ground and then kicked again when he got up , sworn at and called a "r**d ( I was disgusted by that and don't even want to write it) shoved into a wall and sworn at and hit around the face.
All of this in a "naice" very middle class , outstanding school.
And my DS is one of the biggest ( tallest) children in school even though he is in Y4. I think that's part of the reason why he is targeted ( it's always y6 boys who attack him)
I emailed the headteacher the first time it happened and again the second time. The third attack was by a boy who I know has been in trouble for terrorising and beating up my friend's son so I called the school and spoke to the deputy head. ( I didn't tell them that I knew about this boys reputation)
He told me that he had worked at the school for years and had never experienced this type of thing at the school. ( and yet I know loads of parents who have complained of this type of thing - one even took her child out of the school) He must think I'm stupid.
It's a farce , they just deny it happens and play it all down to protect their precious ofsted rating.
You get to the point when you think it's not worth dealing with the school and may as well report to the police. If DS suffered the same attack by a 10 or 11 year old in the street it would be a police matter and yet at school it's just accepted as part of everyday life.