My son is accelerated three grades in math. He was homeschooled until the the beginning of last year and then went to a small private school. At the time he was 5th grade age but took all 6th/7th grade classes (it was a combined class) and Algebra I, which had kids ranging in age from 12-16 (and he was 10). He had no trouble with the material or the kids and ended up being one of the top students in the class. He has a brother who is 6 years older, so he is used to teenagers, which I am sure helped.
However, even though he is still attending the same school, we have decided to homeschool math from now on. The level that the classes are taught to (procedural understanding only--"here is an example, follow it" type of teaching) is not appropriate for a gifted student. Nor is the pace--last year they spent a whole semester on the first three chapters of an 11 chapter book (and the first two chapters were review!).
All of this is to say that if your son is that advanced in math and you're already homeschooling some subjects, I don't think that placement in a regular ed math classroom (as opposed to a gifted classroom) three grades up is the best answer. And that they're using Everyday Math makes it worse. Unless you're planning to use the classroom experience as supplemental while you do the primary teaching at home using a solid program (like Singapore math or AoPS), I would pass on this opportunity.
