A skip and movement into a gifted class was very helpful for my DS8. At the bare minimum, you should reasonably expect the teacher in a gifted class to understand asynchrony and be able to target differentiation (of course that is a reasonable expectation, mileage varies horribly per past threads here.)
We also have tuning conversations with DS about better ways to phrase things to get his point communicated. Emphasizing the two-way street of respect mentioned above.
Near-term, negotiating with the teacher to swap in appropriate level work can help (DS had this in K and 1st, helped by having a TD coordinator in the school.) But effort on their should be met by some reward (e.g. compliance, politeness) on your son's side. Enrichment as extra work can feel more as punishmenet. Access to typical elementary online math resources where he could self-pace were also useful (e.g. IXL) rather than sitting in grade-level math instruction.
