Thanks everyone for your replies.
The percentile scores on the achievement test were 99.9 and about 99.7ish on the IQ. Now that I think about it, the tester did say something about it being unusual that the achievement and IQ scores were about the same - as if it wasn't common.
DS loves to take tests and do things like leave the classroom and stuff. He would describe himself as lazy, I think because he thinks that might make him fit in a little better. But he has this need to be challenged and stimulated that even he isn't aware of.
I guess I'm trying to understand if he's just a little brighter than average or if it's something more. Logically, I know what the scores indicate, but at the same time, I think 'what are the chances?'. I know it must sound weird.
Thanks again for all your input.