[Sangetsu]

I work at a private school, teaching all levels, from elementary to high school students. I teach the younger kids without assistance, as (as you said) they are able to internalize it with relative ease (though at early ages most emphasis is on vocabulary, rather than grammar).

For the older students, they also have classes with a JTE, but much of what they learn is still through exposure. Grammar can be taught 2 ways, technically (which is rather difficult when vocabulary is limited, and not at all fun), or through exposure. I focus mainly on exposure through reading. Structure is first learned by imitation/memorization, and the rules explained afterward.

Exposure actually works quite well, much of our memory of vocabulary and structure is retained photographically in our minds. This is evident when I have students read; sometimes they come across a word and read it incorrectly, without hesitation; this is because the word they are reading has an image similar to another word they already know. Since their vocabulary is limited, their mind associates the image of the word to one which is familiar to them, and they speak out that word.

The smaller pictures (individual words) are easily learned this way, and in time, so are phrases and sentences. Correct grammar can be learned indirectly through this method, so long as the students study and practice regularly.