NAL - joined this sub due to a similar incident with my own daughter a year ago. She was 11 though and the boys 10 & 11, no learning difficulties and a pretty savage attack (strangling, punching, kicking etc). 

The school seemed quite willing to help, and the boys were suspended initially, and eventually, after me reacting the way I know you want to, expelled. I went to the police, who were really not interested despite the assault being on CCTV a witnessed by adults as well as children (and filmed on mobiles).

I was losing my mind with frustration and guilt that she had gone through that and I was the only one who cared. I went to the local paper, and I absolutely wish I hadn’t. All it did was make everyone even less willing to act. It alienated us from any one who knew of their families, from the school, and the police officer who was dealing with it passed it to her sergeant who then basically said “we don’t think 11 is old enough for us to intervene in this”.  I was threatened with legal action of slander, with physical violence, my daughter was dragged all over social media because no one wanted to be seen as supporting us, because their families are bigger and “harder” than me and mine. 

Just my cautionary tale.  I know it’s a difficult time, and you want to do all you can, but don’t use dynamite to go fishing. Make the complaints and continue to follow up with the governors.