I think Cricket2 has some really good points.
It really sounds like your son is throwing the test somewhat, which must be maddening. But I am similar in attitude to Cricket2 with my most 2e child, in that every time I feel cross about results that I think are an under-estimate of her true potential I remind myself that her uneven performance on tests reflects her uneven performance in life. Yes there IS a degree of ability in there that isn't captured by testing and it IS maddening. But conversely that's the reality of her interface with the world - she does often get along very well with HG/HG+ kids, boys in particular, quirky/2e boys even more so, but she's not ready to share a class with them so much as ready to climb trees with them...
In her case she's very compliant and doesn't throw tests so we at least know she did the best she could with that test on that day (most of the time), even if I feel that the test is maybe hiding/missing some of what she knows/can do. So you've got another level of frustration in there - but the same lesson is maybe applicable. If this is how he responds to testing is it indicative of how he would respond to a normative classroom? If so, it sounds crazy to put him in one, a different solution to his social needs is perhaps a better idea.
