So you’d punish your child by moving them from their friends, and from a school they’re otherwise happy, and presumably doing well in….?
Into another school where they don’t have friends?
And if it happens again? Keeping moving them.
Sounds sensible…. 
My children wouldn’t punch anyone either. But then again, they’ve never been provoked in the way the OP’s child has been. Lucky me and lucky you, right?
One of DS’s best friend’s came up against a bully - also in year 6. I’m good friends with his Mum, and it was a really stressful time for them.
He turned the other cheek, and turned the other cheek, until one day he didn’t, and threw a punch back.
He was left alone from that day forward.
And he’s never hit another child before, or since.