I think some of this is school dependent- but my kids were way ahead in Lexia. My middle kid finished it in 4th grade, and then at some point was allowed to move to Power Up, which I think is the MS version.
They do separate classes starting in 3rd for AAP, though your child does have to qualify (even a very high IQ isn't automatic, though if you have outside testing, it can be more persuasive).
I've been impressed with the curriculum my kids have been exposed to in AAP. But I'm pretty laid back about schooling, and just want my kids to be challenged from time to time while mostly enjoying what they learn.