I really feel for you. I have had huge issues trying to get appropriate services from the district for my gifted/AS/dyspraxic son. You do have a right to ask for an evaluation regarding the need for "assistive technology".
Talk to the ESE coordinator at the school where your son gets therapy, and then follow up the conversation with a request in writing, something like "This is to confirm our conversation on (date) where we discussed that I am requesting an evaluation for DS regarding the need for assistive technology and related services."
If they provide your son with assistive technology, be aware that the school may try to drop OT at that point, claiming that the accommodations of keyboard and text-to-speech software bring his functioning up to the level where he doesn't need OT. There are a few routes you can take to fight this, if it happens, including requesting an outside evaluation at public expense if you disagree with their OT's assessment.
Best of luck.
