It is not that there’s no value whatsoever in formal study of grammar. It might come in handy if you want to be a linguist, an editor, a high-level writer, a lawyer, or the like. If students want to take a grammar course in high school or college that seems okay with me.
It just doesn’t teach basic language fluency.
Native speakers don’t start studying grammar until they have had 10+ years of full-time experience with the language. And anecdotally, the students who spend a lot of time reading independently don’t really need the grammar lessons (they already have a subconscious understanding of what is or isn’t grammatical, and the typical school grammar lesson is very slow and obvious for them), and the students who don’t spend any time reading independently and regularly speaking with educated adults would get more value out of instead spending the time reading or listening to someone read. YMMV.
Untrue; formal grammar instruction begins not later than first grade in many curricula, which is age 6-7, which would require using the language several years before birth to reach 10+ years prior use. Native speakers begin studying grammar about as soon as they have the intellectual capacity to comprehend the concepts associated with grammar.
When primary schools try to teach grammar it is boring, stressful, and generally unhelpful to the students.
The dominant factor affecting students’ reading comprehension and writing ability is how much time they spend listening and reading, especially to material which is at an appropriate level to slightly stretch their abilities.
If schools want to spend a relatively small amount of time formally teaching grammar to 12–17 year old students there’s nothing inherently wrong with that, but it’s mostly only useful insofar as it attaches names to concepts so that students can have conversations with each-other about what makes communication effective of ineffective, or more explicitly discuss their existing subconscious grammatical knowledge. Formal instruction in grammar (or other kinds of formal analysis) is still no substitute for practice listening and speaking and reading and writing (ideally with effective feedback), which should be the main focus of language arts instruction.
Maybe we need to bring back grammar school.
I am not knowledgeable enough about the topic to say how efficient or helpful medieval Latin schools were at teaching Latin as a second language, but the idea of “grammar” as part of the “trivium” (alongside logic and rhetoric) meant something substantially different than the modern usage of the word.
On the other hand, once you know a few specific instances, it's helpful to explicitly point out that they're governed by the same rule and give an abstract statement of how the rule works. That way you can check yourself without relying on a teacher to point out your mistakes.
The first time you see an example of the rule, there's no need to explain the rule yet. You can just memorize the example. The same is probably true of the second and third example. Explaining the rule only makes sense once remembering the explanation becomes easier than remembering the set of examples you need to know.
When I'm into a new language I can learn 20-50 words a day, sustainably. Short term more.
By the time a child is 2.5 or 3 years old they can be learning dozens of words per day.
The most efficient way to teach new words to kids is to spend as much time as possible reading books with them.
That said, brute force practice work reeeeally well for language. And naturally people will build a kind of internal grammar anyway. But knowing what is what can help with that too.
That's by necessity because you can't explain perfect tense to a newborn.
Speaking from experience, I gained basic conversational fluency in Spanish from English in a few months by spending a ton of time with LingQ (essentially reading and listening to untranslated passages and creating digital flash cards), obsessively practicing pronunciation, and listening to lyrics in Spanish music for hours on end. I focused on grammar to the extent that I had to, but no more than that. For instance, I learned only those conjugations I actually needed for simple speech. I compiled the ones I needed to study based on what I actually encountered in real passages.
Now, by no means did that render me fully fluent in the language. But, case in point, I took two years of Spanish instruction in school with lots of grammar front-loaded and I gained more or less no speaking or listening ability at all. For me there was a dramatic difference in efficiency between the two approaches to language learning.