My other challenge is getting any sort of accommodations (if attention issues are found). My kid does do a whole lot better in quieter (and small group) environments, as compared to a large group (though his coping skills, even in large groups, is getting marginally better). Would you mention this to the new teachers, if you were in my place ? Or, would you wait for them to gauge for themselves ? For our current school, we did the evaluation based on his preschool teachers' feedback (we knew he was advanced, but they said something else was also going on. His K teacher thinks it is attention issues).
Again, just speaking for my kids' school, there is almost no differentiation for lower elementary. There is some for reading (they use Accelerated Reader, which allows kids to read books at or near their level), but otherwise math, LA, and other subjects are one-size-fits-all. GATE in our district doesn't start until 4th grade.
California schools are also strapped for cash, despite promises that more money is coming one of these days. There will be no incentive to put your son in a small group environment unless he needs serious accommodations. Some schools are amenable to outside testing, others aren't. My school was resistant to testing DS; even though he was clearly unhappy and becoming a behavior problem, he was doing fine academically and therefore didn't fall under the criteria for testing (again, it's a money issue).
