I took music classes from age 10 through age 16 and was never taught about the circle of fifths. I was taught major/minor, key signatures, time signatures, sight singing (pitch and rhythm), piano, bassoon, harmony, inversion, counterpoint, and more, and I recall most of that, but I recall nothing about the circle of fifths. If I had been taught it then that would be odd, because it so matches my interests as a mathematician. I can only conclude I was never taught it.

YMMV. I don't claim that people weren't taught it, I only say that it isn't taught to every primary school student. I know the claim was "This stuff is taught in primary school." and that may be true, that it is taught in some primary schools. I'm saying it's not taught in every primary school. Maybe it's an American thing.

I thought it was interesting, and that there would be Hackers here who didn't know it and would be something that "... gratifies one's intellectual curiosity."

Hence the submission.