Hk, there is a letter from some sort of Federal Agency (don`t recall who) regarding disability harassment and the fact that it is illegal. What you are describing is disability harassment. It is illegal according to federal law, just as harassment due to race, religion, sexual orientation, etc. is. Disabled people are a protected class. I posted an old letter from some sort of federal agency about disability harassment on the old board. Then someone posted an updated link with a more current letter. Perhaps someone can find it on the old board and re-raise it? I posted it under School Resources. I think ajasfolks might know where it is. I think this letter should help you a lot. If it were my child, I would stop referring to it as bullying, and start referring to it as disability harassment or harassment due to disability when communicating with the school. I was disability harassed when dd was in first grade. I copied the letter, wrote a letter to the principal about how disability harassment is illegal, and that took care of it.
ETA: I have the hard copy of the old letter filed away somewhere in my house. If no one can find the link, I will look for the letter, and can probably figure out what exactly to google to find a link to the letter. It really spells out that the school is not legally permitted to tolerate disability harassment.