What we can do with written language can be very different from what we can do with spoken language. When we write, we have time time to hone and craft the language, and so the grammar of writing has some differences from the grammar of real-time conversation or speech.
If we don’t immerse student into great writings, we leave them to fall back on what they intuitively know about language, and as a consequence they simply write like they speak.
And studies confirm that the language of children’s books is richer and more complex than the most of spoken language of even college graduates. Thus, children experiencing great children’s book is an unparalleled opportunity to expose them to sophisticated language, vocabulary, and broad knowledge.
That’s why the time in language education is best spent for listening, reading and discussion around great books, and secondarily on language-rich activity rooted in those things.
In my own experience, teacher comments (including mine) on students work (their speaking and writing, etc.) may quite often be vague, too informal, or too colloquial, too chatty, rambling, or repetitive. Students need more meaningful direction than this. They need immersion to great writings and story-telling, language-rich conversations and meaningful comments to actually grow their whole language competence.