I question this too because my ds9 doesn't think big deep thoughts like some HG kids. He just plows quickly and easily through stuff (and might already know stuff)...his rate of learning is head spinning...like super absorbent paper towel. He could easily do 2years of curriculum for every one others do with an occasional grade skip thrown in for good measure.
So on one hand I see his rate of learning as being exceptional. But on the other hand I see him as pretty similar (just a tad sharper) than his peers in many ways.
I am already stressing about next year and this year is only 1/4 done (on Thursday).
