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When I was a kid in a public school system in New Hampshire, we started serious studies of grammar in 5th grade and continued through 10th.

Interesting. I recall virtually no grammar instruction, other than what I learned in French class. Parts of speech, yes. There was a brief unit on diagramming sentences, which I found annoying.

Of course, we did a lot of writing 5-paragraph essays, and we edited each others' work. But serious studies of grammar? Not at all.