Tom - welcome!
Probably more questions for you than suggestions just yet. First and most importantly, what is in your son's IEP re: behavioral management and interventions? Have they done a functional behavioral analysis and is there a behavior intervention plan in place, and if so is it being followed?
Have these behaviors always been going on or has there been a change recently? What type of a classroom setting is he in - self contained class, self contained building, or mainstreamed (with- kids with-out disabilities)? Does he have a 1:1 aide?
Are you having to deal with the same behaviors at home?
Communication is a huge issue in my humble opinion - I have a nonverbal kiddo as well. Has your son been evaluated for assistive technology/augmentative communication and by who? What type of assitive tech are they using (picture boards, communication devices, etc)?
The school district cannot simply throw him out due to behaviors. They are required to educate your son. I'm assuming he has an IEP, and that affords him protections especially if the behaviors are related to his disability. Has he been suspended, for how long? Has the district explored other placements? Have *you* explored other placements? If the district cannot handle him in current setting, then they must find another more appropriate placement. If one doesn't exist in the district system, then they have to start looking at private placements - they may holler about it, but they really don't have a choice.
Have you contacted any Special Education advocacy groups in your area? If not, I would strongly suggest it. It helps to have someone in your corner when you're dealing with- a SD who is threatening to throw him "out the door", because they simply cannot do it and sometimes it takes some assertive persuasion to get them to see that. It's sometimes hard to be a good advocate when you're the parent - that's why another body can really be helpful.
Again - welcome!