Of course it's important to try to do whatever we can to get the best educational environment for our individual child.
Testing is also a completely reasonable way to assess someone's current skills in particular areas.
However, there is a difference between _ability_ and _identity_. So far as I can see, the history of IQ tests, and even the term "gifted," are based on conflating the two. This worries me.
First, for the epistemological reason: although individual differences among people exist in all traits, the cognitive traits we really care about are almost impossible to measure. Second, ethically: whereas I consider it entirely proper to segregate people according to what they can DO in very specific contexts (like math class), people should not be segregated based on judgments about who they are and what their potential is. We must acknowledge our limits in knowing these things.
My perspective is (and this is primarily as a parent in a similar situation, not one who has gone through the whole process already), if he's not being challenged in school, and you decide that a different environment would be better for him, and you need to do the testing to get in -- then do the testing.
You don't need the testing to confirm what you know. Your intuition is far better than a test or battery of tests. Apart from the practical uses of additional tests for getting into school, I can't imagine that the tests aren't going to tell you what you don't already know. If he had scored 100 or 150 on all of the tests, IMHO it shouldn't change your decision-making process one iota.
