Yes, I agree with Portia-- figure out what strategy will work best
when your child begins studying geometry or algebra-- the reason is that state requirements
can shift UNDER YOU when your child enters high school.
That is, credentialling via something other than afterschooling probably isn't optional, firstly-- it's going to HAVE to go onto a transcript somewhere somehow--
but also, make sure that geometry and algebra II are on that high school transcript.
Why? Well, because "four years of math" is often the oversimplified version of the following:
Math:
Four years*
* at/beyond the level of algebra I, and must include geometry.
Yes, this really
can mean that your child with AP calculus can be denied a high school diploma if they took geometry as an 8th grader and it didn't get onto a high school transcript.
So in short, I agree with your set of concerns-- and I'd be wary of doing too much of this as
homeschool/diy enrichment, because you'll lack the credentialling that is necessary. Please note that credentialling is no indication of quality, of course.