I wonder if you have any visiting specialists for your DC's sn needs...such as edpsych, camhs, salt?
I'd be pulling them in and sending each of them a detailed synopsis (emails will be perfect)...that just looking at the incident recordings in school will highlight what is a very obvious 'pattern' of behaviour from 1 (or however many individuals) being involved regularly/and long standing with this on-going situation and the schools apparent lack of ability to address these issues effectively to put a stop to them.
do you have a statement of needs and are these needs being met?...as per the Dx and what's meant to be in place?
I would be quoting GIRFEC (getting it right for every child)look up childrens act...I would be talking about 'thriving' and not just managing/coping with the environment and the apparent lack of care for the protection of your child, etc The impact and issues this is having for your DC and in addition to the sn has no realistic ability to cope with these situation's alone and (quote sn issues and difficulties)tell them about anxieties and fears, difficulty getting DC to school, etc
That you have kept details yourself of incident's and your child has scarring from 1/2 of these you can access GP and hospital records to make available to provide any evidences needed to support your position.
That you have discussed this every time you have been able to find out from your DC (as school have several times, failed to inform at all) and upon further investigations have been dismissed, not taken seriously, by school and they have been unable to stop this from continuing as school are barely willing to acknowledge these issues
ALL of these people have a duty of care to your DC and ALL must act to resolve this issue....
This is exactly what I did when my DS was suffering from a certain group of kids at school...repeated attacks, teasing, awful things and always the same 3/4 manes involved.....I set about as I have said above...and magic!!!...school HT very embarrassed, could barely look me in the eye, bullying stopped and peace was restored...mostly....Ed Psych took over the meeting she had arranged...HT was quietly in corner and actions were most certainly taken from that point onwards...
Tell them all...report everything, quote the childrens act and GIRFEC (though perhaps that is a Scottish one but England will have same under another name probably)
Deep breath and get firing on all cylinders...tears later when you get through the battle....don't let the bstards pull you down...keep coming out fighting...all strength to you as I know what this feels like and how gut wrenching and heartbreaking it is...but...you have to fight so load up those big guns, research your childrens act stuff and put them in their fxxking place....and breath xxxx