Your DC is working >2 years ahead and I would push for differentiation. Also check with Iowa Acceleration Scale.
But implementing the real differentiation is hard in a classroom. The teacher will give only 1 instruction of all the kids and your DC will get an advance level handout/ worksheet to do it on his/her own. There usually are no instruction for the worksheet. (although those are usually not hard up to 5th grade level).
It didn't work for my DDs. They were asked to do Khan's Academy Math in the library during Math class and we changed school after that school year.
But you should ask them and see what kind of accomodation they are willing to provide.
