As well as a sympathetic principal, you need to team up with an excellent gifted coordintor. That's who's most likely to be designing the IEP and advocating for your son. When you check out the schools I think it's important to find out how knowledgable the coordinators are and whether there are any you could work happily with since your son's education is going to require on-going adjustments.
Have you looked into Alpha elearning?
http://alphaed.org.nz/aboutus.htm It didn't suit my son at the time when we had our trial but I know other people who it has worked for.
