No effing way? Sue their ass!

you need professionals to get involved and see your son's potential

That's absolutely horrible! :(

Keep in mind, they are under-staffed.
They are not 'Experts', they are there to 'Help' your child, not dump them off at their easiest/earliest convenience.
It seems the environment that your child is supposed to learn in has become 'Toxic' and that's on the instructors, not your child.
Don't be afraid to point these things out to the staff, the principal and the school board.
Seems that they need to be retrained on how to handle 'Special Needs' individuals.
Send a letter to the School Board, then 2 days later send a copy of the letter to the principal of the school.
They have sworn to do a duty, and that duty does not include making your child suffer or abandoning them as quickly as they can.
There are resources out there for both you and them, and they are supposed to be trained in that aspect.
So, for them to make 'Diagnosis' on your child is beyond their position and if they have that attitude about teaching, then they don't need to be teaching.

Sounds like you have a pretty steong case. Comsult with a lawyer.