It’s rare for a native speaker of English to write a sentence that is truly ungrammatical. The errors that most writers face are at the level of syntax and, especially, usage. Where do we put commas? How do we integrate quotations into our sentences? How do we maintain parallelism in lists? Those kinds of issues are unimportant from the perspective of the ideas expressed, though they can reach a point where meaning is obscured. They are important, however, to the reception of a writer’s work, to how seriously it is taken. Fair or not, a pattern of haphazard deviations from standard written English undermines a writer’s credibility — and so teaching students how to overcome those problems is very important.
I must admit, though, that I’m not quite sure how. In fact, sometimes I despair that if a person has not picked up an eye for such details by a certain point in their life, it’s just not a fixable problem. I can spot-check and explain things if students seem to have one or two recurring problems (which is already a privilege, since my class sizes are very small), but if they have more comprehensive difficulties, what does one do? I’ve written before that one can’t have real conscious control over comma usage without understanding the grammatical structure of one’s own sentences, a rule that I would extend to most if not all syntax and usage issues — but sitting them down with a grammar book hardly seems to be the answer.
As I reflect on my own experience, it seems that the point where I really began to understand English grammar was when I began learning Spanish in high school. I’ve heard similar stories from others, and it makes sense: you’re forced to think about grammar because you can’t fall back on your native proficiency. Perhaps this is a good reason to include a foreign-language requirement in high school and college — not to learn to speak the language (which is almost impossible to achieve through classroom instruction alone), but to learn about language “as such,” to gain the distance necessary for reasoned reflection on grammar.
Yet that seems unsatisfactory for a lot of obvious reasons. I’m hardly going to tell the student who has more comprehensive usage problems to go learn French and get back to me. What do others think?