Can you ask about subject acceleration just for math? DS8 was sent to 5th grade for math and then was sent back when math was over. He is obviously not as mature as 5th graders but they just worked around that (luckily his school has been very flexible...in the past we have dealt with schools that were exactly like yours). Subject acceleration is something that it's best to plan before the school year starts because they will need to align the math schedules of two different classes.
Before DS went to that school, I advocated for him to be allowed to do Khan Academy on the computer during the second grade math. It has video tutorials for each unit as well as practice problems with tips/hints if he got stuck (if a kid gets stuck they can keep clicking on hints until the problem is basically solved for them). The teacher had asked for all computers to be removed from her classroom and I found out after a few months of school that she had been having DS do this on a mini-ipad (and only a couple times per week). DS wasn't coordinated enough to make it work on the ipad. He also didn't have access to any scratch paper. The teacher wasn't monitoring what he was doing at all. I asked for DS to be able to leave the room to do it on a real computer under the direction of a spec. ed teacher (DS has an IEP) and the classroom teacher made a huge stink. That's when we took him out and put him in current school. Anyway, the Khan Academy solution isn't ideal because obviously it's better for a child to have instruction from a real human, but it's better than nothing.
For reading, I sent in books like Harry Potter for DS to read in class rather than the low-level books that were there, and that solved most of the reading problem (again, no direct instruction though).
It's easier to advocate if you have test scores. DS was 99th percentile for both math and reading but it didn't end up mattering at the last school. The teacher was obsessed with the idea that he might have gaps. Current school on the other hand used that data to accelerate him for both math and reading. They assessed him at a reading Level V and instructed him at that level, whereas the other teacher a month or two earlier had assessed him at an L and I don't think he was ability grouped for reading even at an L.
