Very good question, and good you addressed this. There is certainly advocacy for this situation, and the problem can be more wide-spread than one might suspect.
First, that his school is not allowing a Service Dog is technically illegal - they simply do not have the authority to do this. But in any case, his mum, dad, or another caring other (maybe MizLiz) can go to either your local Disability Law Center &/or DVR (= Division of Vocational Rehab) & ADA (American's w/ Disabilities Act) - DVR/ADA are linked. Also the boy's medical provider can give verifcation to facilitate this process.
If the family can afford, then they may go to a private lawyer. Also, the local chapter of Easter Seals, NAMI, local state representative (or ombudsman) and your local United Way. And contact dircectly the School Board (not the principal or teacher who doesn't know a thing).
Disability Law will assign a worker and this can be fixed! The family (& dog) can get a license that is above & beyond whatever school says - they're out of bounds. Also, check into the place where he received the dog; that agency ought to be able to direct family to go for authorization. He can carry on his person a license and the dog as well.
Believe it or not...this has happened: Autistic individual w/ Service Dog was using the public bus system (yes! Service Dogs are allowed on the public bus - that's what they're for). He was told he could not enter the bus with his Service Dog (the Dog has his service vet, etc) by a BUS DRIVER!! That driver has no authority whatsoever. Situation was fixed, but the guy had to walk, then someone called a cab. Geez.
Sometimes people (who have NO authorization whatsoever) feel that Service Dogs are only for the blind. Wrong. And it's none of their business anyway.
I hope that helps - he needs that dog.
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The ones who say “You can’t” and “You won’t” are probably the ones scared that you will. - Unknown