I don't think that a parent can make a judgement on the curriculum or class content in a classroom. In the schools that we have been in, there are administrators, Head Teachers, State standards, Common Core, Curriculum committees etc that have dictated what needs to be taught in a classroom. Sometimes, they identify the material that they can use at the teacher's discretion for differentiation. But, parent bringing in external curriculum for instruction is not allowed and in the local public schools, the parent needs to meet with the Principal to find out how to do this (with PTA and Site Council involvement). Basically, no.
Having said that, I volunteered in the math class once a week in K and had the same frustrations as the OP - what I did was asked for permission to bring in manipulatives or math games and convert part of the free time of early finishers to a math game playing time - we already had things like tangrams and cuisinart at home which I took with me - but, for things like money, the teacher gave me some pdfs and I laminated several copies and cut them out to make manipulatives and we played games with advanced concepts - we called them grouping games, balancing the scale games and skip counting games instead of multiplication, division or intro to equations. We also had a once a month mini Math Bee where all the participants got a sticker and an eraser.
Though it was all fun and felt constructive at that time, my son needed more instruction at a higher level and after-schooling intensively to meet his needs was getting exhausting because of sports and music and we left that school and moved on to one that would actually teach challenging content during school time. Sorry, if your DS is very advanced, you might have to find a school that will teach to his abilities or after-school him or homeschool him. Good luck.
