Are you in the UK? If so, I think your school system is different enough that most of what I've learned about schools here wouldn't apply, but one thing that might is get advice from an occupational therapist about what might best help your son - is he receiving any services yet? Do you have formal evaluation from outside a school setting that might give you any guidance?

There's a couple good books on various aspects of special needs in education that might help you. Have you read:

The Mislabeled Child (by Eide and Eide) - what I found most helpful.

Raising a Sensory Smart Child - also good.

Best of luck to you with process.