We have a child, too, who tests much higher on IQ and individual achievement tests than how she performs in school. It does leave my head spinning at times wondering if she is really that able b/c she sure doesn't appear to be in school much of the time.
In our instance, the issue is further confounded by an older dd who outperforms what we would expect given her MG IQ scores from age 7. In our older dd's instance, I think that her IQ scores were probably a bit of an underestimation, though.
I don't know that I have any answers for you, but do want to welcome you

! Your ds is still very young, though, so it may take time to see what he can really do academically and his areas of interest just may not line up with those things that generally get recognition in school.