We are in just about the same situation. DS10 is in 6th grade math this year and has not learned a single new concept this year and knows almost all of next year's prealgebra curriculum as well. He's never missed more than one problem on any of the tests and we have talked to his teacher about how everything this year is a review. He has even pointed out to his teacher that he did a lot of the seventh grade work last year at a different school (his teacher also teaches prealgebra and DS has seen their assignments). His teacher knows all this and will be giving him a math placement test to see if he is ready for Algebra I next year, and yet, from all our previous dealings with our daughter, we know that the likelihood of his being placed into Algebra I is slim, regardless of how he does on the placement test. My older DD took and did well on three of these tests and yet the school said she couldn't do Algebra because of "holes." Nothing we said could convince them that she actually looked forward to "holes" - that meant she would actually learn something in school. The only thing that worked for DD was for us to insist that we, her parents, would take all the blame if it all went wrong if they would just let her try. We would have signed papers attesting to that, if asked. Only then was the school willing to let her take Algebra I. And lo and behold, she got an easy A and had fewer gaps than many of the kids in the class with her who had gone through pre-Algebra.
So, anyway, we are in the same boat with DS right now, and preparing for resistance from the school. You would think that if a kid liked math and was good at math and wanted to learn higher level math that the school and teachers would be thrilled and at least encourage the student to try. The other pipe dream would be for math teachers to become mentors to such children and actually encourage them!
We also had a similar initial situation with #1, but a more positive overall resolution. In 5th grade, we asked for a grade advancement in math, but were told that since assignments were not being completed any faster than anyone else, no subject acceleration was needed (never mind that #1 was filling in the time by chitchatting with classmates, helping other people with their work, etc.). To be fair, the school had just done a whole grade skip, so they probably figured that that was enough. Fast forward to November of sixth grade, when the (same) math teacher came to us and asked if a straight skip to 7th grade math (from Saxon 7/6 to Saxon 8/7) would be okay with us. We did it, and saw no dip in test grades from the high 90s. By the spring of that school year, the math teacher was the one recommending algebra I for seventh grade, where #1 had the blessing of receiving instruction from a college math professor who was doing some part-time teaching (this was his only class, actually) in this small private school.
I think one of the factors that helped is that this school was using Saxon at the time, which is very much a spiral curriculum, which helped the teacher to feel more comfortable that any gaps would be filled along the way. She also had a mathy kid of her own, and was more sympathetic to making modifications.
Sometimes you do encounter schools that are willing to bend a little, and teachers who want to encourage capable children.
