Many years ago when I was teaching English at a small rural high school and was English Department chair, my principal cautioned the entire faculty about our students' scores on the language part of a national standardized test: "Before we look at our language scores, remember that we don't teach grammar in our English department."
He even made an effort to make eye contact with me and gave me a slight nod and smile. He thought this comment was what I wanted to hear.
But, the truth was that most, nearly all in fact, of our English faculty still taught grammar in isolation and required their students to write very little (one veteran teacher taught strictly by the exercises in the grammar text and required his seniors to write one, yes one, essay due at the end of the year, and that was it for writing).
And the few of us who were focusing on writing and addressing grammar, mechanics, and usage authentically (in the context of our students' writing)—basically me—were teaching grammar.
And herein lies our problem. . .
So when we hear anyone talk about "teaching grammar," we should pause and help clarify a few things:
(1) Few people have any real need to learn grammar (or any of the conventions of the language) as a goal itself. If a student or adult wants to be a grammarian, that is fine, but the conventions of the language are rarely our true goals in the ELA classroom. We more often actually want to raise the literacy of our students, and that goal includes grammar (or conventions) as a skill that contributes to that larger ends.
(2) Few, even teachers of ELA, have 100% proficiency in the language. So we often over-exaggerate the weaknesses our students have in conventions and underestimate how much people know about language since much of our language "knowledge" is at the usage level, not at the explicit level (similar to our being able to drive without being able to name the parts of a combustion engine or being able to dismantle and reassemble that engine). Humans need not be perfect in the conventions (which chnage, by the way) to be highly literate. But humans do need to enjoy and value language to grow in their literacy.
(3) But. . .those of us who teach writing and address literacy should all work on our understanding of the language. We must continue to grow as writers and continue to hone our understanding of the language. I recommend highly Style by Joseph Williams.
(4) And we must know the research on addressing grammar and conventions as a skill that leads to stronger writers. For this, you must begin with Connie Weaver's Teaching Grammar in Context.
So we must be careful how we talk about and help others understand that for many decades we have flipped our approaches backward—believing that since strong writers have strong grammar skills (which isn't even true) that we can force grammar in students and magically make them good writers. The irony is that writers are made by WRITING; the writing and revising, especially in a workshop and process setting with a mentor teacher guiding, will gradually raise the grammar and conventions of the students. As Lou LaBrant wrote more than five decades ago, "Writing Is Learned by Writing"—and that includes the conventions of the language.
Here is a great resource:
Summary of research and guidelines from Fox Valley Writing Project (Word doc download).
