I faced a somewhat similar issue with a child with ADHD. In our case, though, we weren't moving, but had encountered difficulties at the elementary school and wanted to make sure that the proper issues would be addressed in secondary school. I eventually became very involved in the national group involved with ADHD--CHADD (Children and Adults with Attention-Deficit/Hyperactivity Disorder)--and served as the coordinator (the top elected officer) of CHADD of Northern Virginia, the second-largest chapter in the nation. And we have parents every day asking the same questions.
First, contact the national associations most appropriate for your son/your son's condition. It might be the National Autism Association at http://www.nationalautismassociation.org/
or the Autism Society of America at http://www.autism-society.org/site/PageServer
, or possibly another group. You may already be involved with such a group. If not, ask your pediatrician for a recommendation.
Then contact the local chapter or branch of the national organization. Talk to the head of the local group. Be as direct and blunt as you need to be. Most chapter heads will be very willing to be very honest about schools and school districts. As you've probably found out, it's not just the school district, but the individual school. Our own problem at the elementary school was caused by one person: the principal. Many of the teachers were helpful and supportive, but the principal refused to believe that there was any need for any special education programs, much less that ADHD exists. (Yes, I know there's debate about that, but there's something going on with kids all along the autism spectrum--from autism to Asperger's to executive functioning difficulties in ADHD kids.)
At any rate, you should be able to get some straight answers from the people "on the ground" in the area. Also, take whatever steps you can to get your son qualified for an IEP, if he isn't already. And be wary of 504 plans. They actually can be very helpful, but sometimes schools will tell you, incorrectly, "Oh, you don't need an IEP. We can accomplish all that with a 504." Untrue.
And arm yourself in other ways. Some school districts have excellent special education programs; you can tell a lot by what they post online, and what programs they offer to parents to help deal with the issues. Oh, and when you're talking to the local chapter head, also get the name of a good special education lawyer. Hopefully, you won't need a lawyer. But if you do, be prepared.
It really all comes down to: Talk to people who've been in your position before, and have already gone through what you're going to face. And, with all due respect to all the other Realtors here who understandably shy away from questions about "best schools" with advice to "look at online resources," the online resources (number of special education kids per school, for instance, or even ratio of special ed teachers to students) will not--repeat, will not--tell you what you really need to know. Please trust me on this.
Hope that helps. And post any other questions here, or feel free to contact me.