A few quick thoughts (and our son is the same age with the same trait as far as resisting then embracing change once it happens, btw!):
-I wouldn't necessarily do pros-cons as in my experience focusing on the benefits works best with our kid (not hiding the cons but simply mentioning them then moving on)
-Would the school agree to a "trial run" of say a month or six weeks? That can take some of the pressure off the decision.
-Perhaps looking with him at the more advanced curriculum vs. the rest of this year's will help. That really got our son excited, to see that he would be learning some new things.
-It helped our son to hear about other kids who were also accelerated. We had two examples from the school that, ironically, we had to pull him from... but at any rate, they were boys he admired and that helped. My mother was also double-accelerated so sharing her story made it seem more normal. His father and I shared our stories of not being accelerated and being bored...
-We talk about developing learning habits and that staying in classes where you already know the subject matter well doesn't build those... and that waiting until college to build those muscles is tougher.
