Can you talk to current first grade parents and see what it is that the most advanced kids actually do? If you don't know which parents to ask, then actually ask the teachers to show you? That would probably give you a better idea of whether it will work. Personally I haven't seen a teacher yet who has been able to make in class differentiation for math work out. The best anyone could offer was to give him independent worksheets that no one else was doing, and put him on the computer to do programs like ixl or Khan Academy. It was better than nothing but the acceleration has worked a lot better. So in second grade started to go to a 5th grade classroom for math. Now in third he is going to 6th grade. The problem is now what? Everyone in his 6th grade math class is going onto middle school. Someone will now need to figure out how to do in class differentiation, but at least he got 2 good years out of an acceleration (luckily he is about to enter a class where all the kids are highly gifted so my hope is that there are other kids close to his level). I would do an acceleration if possible and you can always switch it to differentiation in class later if there is no where for him to go.
