Do you need to change his grade designation to do more difficult work?
Well, looking at my question now, I can see why you would ask that. No, I don't care if he's "K" or "6th" when we tell people. That's why I never pushed to start him early and held him back from K as a 5 y/o (which happened to be a mistake

) I think it has been in my mind that we will eventually need to give him a more accurate grade level name. Why? I don't know. LOL
Is your son happy and comfortable being challenged? I think having time to think and explore areas of interest can be great for these kids if you're looking for ways not to race through grade levels.
No, he's not comfortable being challenged. He's developed this issue where he has to be pushed to do anything that he immediately perceives as difficult. THAT is my concern about not challenging him more than we do currently. If it weren't for math (and anything requiring the use of his motor skills), I wouldn't know what "challenged" looks like for him.
He does have many interests outside of schoolwork. We don't really separate academics from our daily lives too much. We don't have TV or video games, so there's little media taking up his time. He rides his bike, he collects for his natural history museum, he does art, he takes nature walks, he invents things, works in his garden, does some sports, etc. I have been perfectly okay with this kind of life for him --for us.
I suppose my concern arose when it was suggested to us that his lack of focus, his resistance to trying things he perceives as too difficult, and his achievement scores being less than 99% in math were due to me not challenging him enough by presenting new material when he was ready for it.
So, do I ignore what we were told by the doctor? Do I keep going along like we've been doing and let "okay" be good enough for him? I don't know where the balance is at this point and that's what scares me, but I do believe that it will all work out in the end. I'm just trying to gather info and gain insight in order to get a game plan.