We took our kind and sensitive 9 year old DD out of school following repeated instances of physical bullying by a group of boys in her class. I emailed the school with details following each and every incident and met with the Class Teacher 4 times and eventually with the Head, to try and get something done about the children involved.
The Class Teacher was next to hopeless, which I was stunned by, as she had been teaching the same age group at that school for the previous 25 years, so we fully expected a robust approach. Her "advice" was basically "Tell her to ignore them, walk away and tell a Teacher", which, of course, she had already been doing but was still coming home injured and tearful - the final straw was bruising all down her spine where they had beaten her across the back with bags containing their studded football boots. The Teacher refused to even call the boys' parents about the issue, saying "They just aren't engaged with school at all, their parents let them play Fortnite and 18 rated games, it's an issue with lots of children these days I'm afraid..."
We pinned our last hope on the Head, but she felt that she didn't want to 'encroach' on how the Class Teacher was failing to handling the situation.
So we took her out of school. I told them that as they could not keep her safe on school grounds, I would look for an alternative school for her. Happily, it was only a few days before Feb half term, so I did lots of phoning around and took DD to have a look at a couple of schools which had space for her and we chose one where they had a very clear Anti Bullying policy, and a calm, friendly environment. She was able to start there right after half term, so only missed 3 days of schooling. She joined them halfway through Yr 5 and finished Yr6 there happily, having made some lovely friends and never once coming home in tears or injured by another child. It seems such a simple thing to be grateful for, but how awful for our DC who have to go through these episodes of bullying, it's so damaging and scary.
In your shoes, I would continue to communicate the details of all the incidents to the school, ensuring you copy in the Class Teacher, Head and Safe Guarding Lead and ask them for reassurance that they can and will keep your child safe - and exactly how they plan to do this.
In the meantime, I would put out feelers to find out which other schools local to you have space for your DC, so that you have a back up plan if the current school continue to fail your child. You have to advocate for him.
I was bullied. Not as a child, but as a 38 year old woman, in my place of work. It was humiliating, depressing, infantilising and it destroyed my confidence in my work, which led to me making mistakes. The sense of dread I felt as I walked to the office was so bad, I often had to run straight to the bathroom to vomit. This all happened not terribly long after we had changed our DD's school due to her being bullied, but I found it nigh on impossible to admit to my DH that a similar thing was happening to me - I felt pathetic. I let them 'manage me out' without putting up a fight, and the sense of relief was enormous.
Whatever decision you make from here, please involve your DS with making it, help him to take back a little piece of that control the bullies have stolen from him. I hope you and your family have a wonderful Christmas and I hope that bullies the world over get exactly the Christmas they deserve! 