@fragbot the point you are missing is that the advanced math student is not in a “larger school system” and therefore may only have 1-2 peers. There is no additional instruction available to that student and they are the additional instruction for the students just behind them in ability.
This happened to my DD20 in reading and math until 3rd grade when there was finally 1 hour of higher level math offered 1 day per week. True higher level math was not her daily math class until 4th grade.