I am still trying to understand my options. From what I've read on this forum and discussed with a couple of psychs is that he must go to a gifted or a gifted friendly school. Option B is homeschool. Option C is fleeing. So, I'm having the WISC done. That will determine whether a gifted school is an option. I also need to call around because I now understand that there are gifted friendly schools of all varieties and just because it's a montessori doesn't mean that it's gifted friendly.
The US Public school system is not monolithic - it varies greatly in terms of underlying philosophy.
There are a few very good GT schools from K-12 in major metro areas. I'd look for the parent support groups and talk to the parents to get the information and a "feel" for it.
Some schools will "conditionally" admit your child and then you can move into the district with this understanding.