It sounds like you got the information they were seeking - is he capable of handling the current academic environment. The answer appears to be a resounding yes, with yet another question - is he being challenged enough.
Did they do any additional testing such as academic testing in reading, writing and math? Did he hit the ceiling for these tests too?
Often times special schools like your son's have groupings that are based on learning profile including IQ, learning style and current skill level. My guess is that the school should consider finding an alternative grouping for your son so that he can be challenged and still get the support that he needs for his CP. He deserves both, and I suspect he'll become even more frustrated if he isn't challenged.
You also seem to have another question - what is his actual IQ? In order to get this "number", an evaluator must used a test that is normed for his age. There are some that are better at identifying giftedness (tend to have higher ceilings), and the evaluator should keep this in mind when deciding which test to use.
