I wonder if teaching people analog math would be better. This is more practical if you don't need exact quantities, and more in line with how your brain actually works. Symbolic math isn't "natural" and you learn it not by generalizing but by memorizing a large number of facts and heuristics. But your brain is really good at approximating continuous functions. Imagine how much complex math goes on in your brain when you see a ball in the air, predict where it's going, and coordinate hundreds of muscles to catch it.

I imagine it would work by seeing two bars or boxes and then drawing a third bar/box with the correct area/length and getting rewarded based on how good you do. Another exercise would train you to convert numbers to or from boxes with the same length and at the appropriate scale.