For my boys, we went outside school to various providers of math offerings for gifted kids. But quality is rather variable.
Being ahead academically doesn't mean you're ahead developmentally. Rote practice to avoid mistakes and do really systemic work is useful sometime around ages 12-14 -- during first algebra classes for kids on the normal plan. But courses for gifted 10 year olds taking Algebra I at e.g. CTY tend to lean even more into the "rigor", which my kids survived but it was unnecessarily difficult. Instead, they should be looking for ways to shorten problem sets and approach problems from various angles.
That is, whether you can keep a 9 term polynomial straight and avoid swapping signs or coefficients is really a measurement of attention span and focus, not understanding of algebra... and students that are way ahead in math are probably slightly ahead in attention span and focus, but not to a degree commensurate with their mathematical knowledge.
(We really like Art of Problem Solving, though it's pretty intense).