Ds was at a school for a short time a couple of years ago and was bullied by one boy since he first day. The child was violent towards ds, pushing him into tables (in front of the head), punching him and slamming a door on his hand. He was part of the reason why I moved ds out of the school, his mother collered me in the playground and started complaining that her son now had detention because of ds (this was after he slammed a door onto ds's hand) 
Ds has been at his secondary school since September, he doesn't like it as it's a treck and he's finding it difficult to make friends. The bully walked up to ds this morning and hit him (lightly) across the head and asked ds if he remembered him. It's been a couple of years but I'm very worried. What should I do?