I learned how to diagram sentences in college. It was eye-opening, and I wish I had learned it sooner.
I seem to have ended up with a very strong "sense" for correct english (though I know some parts where I'm weak; and also my online "post a comment" style stuff ends up full of shorthands...). I presume that my "being good at catching grammatical weirdness" comes from several schoolyears learning German, and being a voracious bookworm as a kid.
Curious if that sort of situation is also the case for others who weren't heavily taught diagramming but still feel they ended up being really good at correct written English.