In my underfunded rural American elementary school, they taught us Venn diagrams. Not set theory per-se, but they taught us to read and create Venn diagrams.

In my underfunded rural American elementary school, they taught us Venn diagrams. Not set theory per-se, but they taught us to read and create Venn diagrams. I don't know if that's representative, but my gut instinct is that Venn diagrams are very accessible to the general public.