Reforming the overall approach would probably do more for numeracy than tweaking the end stage curriculum.

As it is now, you have ~3 groups of students in most K-12 math classes. A group that is bored because they have mastered the concepts being presented, a group that is benefitting from the concepts being presented and a group that doesn't have the framework to benefit from the concepts being presented.

There are of course lots of teachers that will be doing what they can to address the gaps, but it needs to be systematic.