In grammar there's only a small body of knowledge to learn--it doesn't need to take years and years to learn it, and it doesn't need to start in first grade. Students will pick up grammar concepts without years and years of formal training if they read books. Trust the process! By the end of elementary school, students only really need to know two rules: (1) Capitalize sentences and proper nouns. (2) End sentences with punctuation (a period, question mark, or exclamation point).
It's also useful (but not vitally necessary) to be familiar with the following so that, when grammar is learned later, these concepts aren't totally new. This is only a suggestion. Don't worry if you haven't covered these, and don't feel pressured to rush out and buy a curriculum to teach them. They can be introduced naturally during routine school reading. All your child needs is to be able to identify these in a sentence: The four kinds of sentences (question, statement, command, exclamatory) and the eight parts of speech (conjunction, noun, verb, adjective, adverb, preposition, interjection, exclamation).
When you begin written narrations, you can introduce more punctuation. Don't teach the mechanics of writing before students actually writing! This might be around year 5 or later. Two years after beginning written narrations, you can begin to focus on style.
The most effective way to teach language arts is to get your child reading their school books themselves as soon as possible. When reading aloud, your child's mind may wander. Also, he isn't seeing the words on the page, so he's not seeing the spelling, sentence structure, punctuation, and he isn't being challenged to push his reading levels. When you read all your child's school books to him, he isn't learning to spell, you are. So read aloud a fun story to enjoy together, but your student should be doing his own reading for school.
Grammar is a very finite subject--like the multiplication table. There's just a certain quantity of information to learn/comprehend. It's very abstract, and that's why we don't suggest more than parts of speech for elementary. You can get through it all in 1-2 years, easily--and middle school (grade 7 or 8) is the perfect ages for it. There are lovely grammar curriculums, and there are really basic get-it-done curriculums.
~Karen (on Facebook, 2018)
AmblesideOnline curriculum does recommend a formal study of grammar
starting in Year 4. This doesn't necessarily mean using the same book
CM used, although that could be a possibility; just as with CM's
arithmetic textbooks, J.M.D. Meiklejohn's or Morris's books may be too out of
date, not appropriate for North American students, or just not fit the
needs of your students. (Besides being hard to find.) That's why we've
left the choice of books and methods open, although we do obviously
have some favourites. But we do want to encourage at least some careful
and detailed study of English grammar, whether it starts in grade 4, 6,
or 8.[Meiklejohn's "A New Grammar of the English Tongue" is online at archive.org; also here.]
May I also offer an opinion as one who had little more formal grammar in school than "this is a noun, this is a verb"? I couldn't agree more with Ruth Beechick that if children hear and read good English, they will be able to speak and write it correctly without knowing what a "bare predicate" is. Agreed! However, for anyone attempting to learn a second language, knowing some of the terminology of English grammar will make it easier when it's time to conjugate verbs, use a past participle, put certain endings on words used as subjects, etc.
Also, I used to type papers for graduate students who could NOT write a decent paragraph (or spell, usually). I would not go so far as to say that knowing about past participles would have helped them much when they couldn't even frame their thoughts coherently. (This is what I think Ruth Beechick is saying too.) However, a basic knowledge of grammar would not have hurt either.
Grammar was taught as a separate subject, beginning in Form II (the junior grades) and continuing through high school, using a traditional textbook (at one time they used Meiklejohn's books, another time they mention Morris's English Grammar; at some point after CM's death her book now known as Simply Grammar was published). If you've ever seen Harvey's Grammar, those books were probably very similar.
I don't recommend not teaching grammar, nor did CM. She taught it quite formally, albeit slowly. In the few sample sections we have, you can see that the children worked through only about 14-20 pages in a grammar book (per term). The fundamental point here is that learning formal grammar will probably not help you with correct speaking and writing--those things are better learned from hearing and reading correct speech.
Grammar will help in some of the areas that others mentioned--foreign language study and tests which many are forced to take. I actually like grammar myself, and enjoy teaching it. <g>
We don't ignore grammar, but I didn't begin to teach it formally until my daughter turned 9. I had some this-is-a-noun teacher's store workbooks etc. (from yard sales) that I was going to use, but I decided in favour of an older textbook (Grammar Is Important, by McGuire) that is very similar to Harvey's and concentrates right away on the elements of a sentence--predicate, subject, phrases, etc. I found this approach worked well--we did it a little each week, mostly orally. We did only the first bit of the book, and I'm planning to continue it this year.
Another book you might find interesting as a writer is Pinckert's Practical Grammar: A Lively, Unintimidating Guide to Usage, Punctuation, and Style, published by Writer's Digest. It is not a traditional grammar text at all; the grammar review is, as it says, practical, and it's sandwiched in with choosing right and wrong words, building strong sentences and paragraphs, arranging ideas and making transitions, revising your writing, and developing "your own personal style", which is really what it's all about, right?
I decided to start with the formal grammar text, but I'm planning on using Pinckert's with my daughter when she gets to junior high age, probably spread out over a couple of years.
Dr. Vavra's grammar (KISS) uses a very slow approach to teaching grammar using techniques which are fairly compatible with CM methods and require only about 5 minutes a day.
CM taught grammar as a separate subject, beginning in Form II (the junior grades) and continuing through high school, using a traditional textbook (at one time they used Meiklejohn's books, another time they mention Morris's English Grammar; at some point after CM's death her book now known as Simply Grammar was published). If you've ever seen Harvey's Grammar, those books were probably very similar.
I'm not sure exactly what you mean by Language Arts, as that's one of those terms, like Social Studies, that can mean a whole lot of things. The process of oral and written narration--not an easy exercise!--covers quite a lot of ground in composition and comprehension skills. If you mean some of the little things like homonyms, they're quite easy to teach informally or in a couple of lessons (online worksheets and puzzles).