Hi Meagle
At 13 years old time is running out to get your son the support he requires - sad, but true.
Is he on Schools Action Plus? - he should be as he is being seen by CAMHS.
Does he have an IEP? - he should have if he's on Schools Action Plus.
has he seen the Local Authority's Ed Pysch? If not he should have as he's being seen by CAMHS. Don't wait for school to refer him, you can ring the Ed Pysch and refer him yourself.
Support at school is not provided in response to any particular dx but is provided to support identified difficulties.
I'm suprised that the Clin Psych at CAMHS was easuring his reading ability etc - that's the role of the Ed Pysch.
I'd be inclined to initiate a request that make lead to a Statement by writing directly to the LA with your request. the IPSEA webiste has some information on how to do this.
School will probbaly try to dissuade you from applying but ignore them.
If you feel the CAMHS Clin Psych supports your view that he requires a Statement, then include the report with your request. If you feel it doesn't then just make the request based on your own identification of his difficulties and state he is already being seen by CAMHS who have noted....
As you know - you don't have time to hang around. The Statement process takes up to 6 months and Statements are not issued after age 16 (statutory school age).
One thing you ca do immediately for him is to write to school pointing out he has OCD and requesting additional 25% time in exams. My son has OCD and has this. OCD interferes with cognitive processing so it could take him longer to read the question / formulate and write his answer. School may grant this or may call in ed pysch to grant this.
Definitley woth doing as he'll get extra time in his GCSEs
Best wishes