We have had difficulty with bullies over the years.
Once my son was pushed so hard into a soccer goal post, he had to go to the ER and have 14 stitches put into his forehead. DS refused to tell who had pushed him because he didn't want to "get the boy in trouble." We eventually got him to tell us, and we reported it to the principal. Also, my DH has a word with the offending boy's father...thankfully we have never had another problem with that boy again.
At another time, DS was having problems with a couple of boys in his class making fun of him, picking on him and kicking him at recess. First, I instructed him on how to handle the problem. When that didn't work, I asked DS's teacher to handle the problem...when that didn't work, I went to the principal. The principal dealt with the boys and it stopped for a while, but then started up again. I, again, went to the principal and told him how serious I was about the issue. He kept an eye on the situation, and with the new school year made sure that the offending boys were not in the same class with DS again. That helped out so much.
My point is, I think it is important to teach our AS children how to handle issues on their own, but when they, for whatever reason, can't get a handle on the problem, then he/she needs to know that you will be there to help them through it. If that means going to the principal, or in original poster's case, the bus driver or bus company, so be it. This is especially true if someone has been assaulted as in the case of my son and the original poster's son. No child, disability or not, should have to go through life being mentally or physically abused and scarred by another person.
_________________
A foolish consistency is the hobgoblin of small minds. ~ Ralph Waldo Emerson