It's taught to young music students. I learned it in public school in the middle of nowhere. Probably age 10 or 11. As did both of my sisters, brother and everyone else in the school orchestra. One wouldn't learn it outside of music lessons or a music program. However, it's taught pretty early on if you're doing anything related to classical music.

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.

I went to school in Germany, where all pupils have basic music lessons. I admit that when I learned it at school, I did not pay much attention, and only really learned it again from taking guitar lessons. Still, it is very, very basic stuff. Not saying it is not interesting, just surprised it makes it here as "news".

  > just surprised it makes it here as "news".

I appreciate your point, but not everything here is "news" anyway. The guidelines state clearly that things are "On Topic" if they gratify one's sense of curiosity. I, like many others, would be disappointed to see too many things posted here under that banner, and I'd be content to have this item flagged as inappropriate, but it seems to me that many, perhaps most, people don't know it, and I agree that it is interesting.

Hence the submission.

As always, this raises interest in, and discussion of, separating "stuff that's interesting/useful" from "news." Personally, I'm not here for "news" so much as "interesting stuff".

It's an interesting issue.

True, if it was new enough to a sufficient number of people, I guess there is not much to prevent it. I was just surprised.