> Native speakers don’t start studying grammar until they have had 10+ years of full-time experience with the language.
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.
There is little if any formal instruction in grammar in reasonable primary schools. All else equal, students who attend primary schools that don’t teach grammar at all end up speaking and writing just as well as students who attend primary schools that try to teach 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.
> Although the term scolae grammaticales was not widely used until the 14th century, the earliest such schools appeared from the sixth century, e.g. the King's School, Canterbury (founded 597) and the King's School, Rochester (604). The schools were attached to cathedrals and monasteries, teaching Latin – the language of the church – to future priests and monks. Other subjects required for religious work were occasionally added, including music and verse (for liturgy), astronomy and mathematics (for the church calendar) and law (for administration).
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.
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.