We had ds14 tested at age 6 at the request of the school. He was not settling down well into the classroom and was behind in reading. We had a reputable psychologist test him all in 1 day with all the subtests of the WISC-4. He also was given some achievement testing. He did ok but did not test gifted at that time. I think that a full day of testing for my 6 year old was too much. He did get an IEP for an LD in written expression and reading.
He was tested at age 8 1/2 with a subset of the WISC-4 (excluding WM and PS testing) and tested 99.6 GAI. We did a psycho-educational assessment, and found out that DS14 is dyslexic, CAPD and has ADD-I. All these issues make it really hard to concentrate for a full day.
I think that for a young kid with learning issues, a full day of testing is counter-productive. Your son sounds gifted to me. Can you find a tester who will do the testing over several sessions? I don't believe you can do a second WISC within 2 years, but you could get another IQ test done once the VT is complete.
