There are those who would say that children don't need much training in formal grammer because they will figure it out naturally as they read good literature and do lots of copywork. Well Lori just had an excellent post explaining how "there exists an inseparable connection between the structure of language and the structure of thought." She included this great quote from Richard Mitchell:
People who have learned even a little about how English works have all heard about modifiers. They know that a modifier is something that tells us something about something, and that there are many kinds of modifiers, some with tricky names. The way we teach things like this, as though they were subject to arbitrary rules like the rules of basketball, is so stupid and tedious that most people block out modifiers as soon as possible. The English system of modification, however, does not exist in a set of paltry rules that do what they can, and fail, to describe some very elaborate operations not simply of the language but of the mind. To say that an adjective modifies a noun is worth nothing unless we see that sticking adjectives on nouns is the outward equivalent of some mysterious inward process that goes on in the mind. It's not entirely absurd to think that somewhere in the past of mankind someone, for the first time, did in his mind the equivalent of putting an adjective to a noun, and saw, not only a relationship, but this special relationship between two things of different kinds. That moment was more important to our history than the flight of the Wright brothers. In sum, all the seemingly complicated kinds of modification in English are just ways of thinking and seeing how things go with each other or reflect each other. Modifiers in our language are not aids to understanding relationships; they are the ways to understand relationships. A mistake in this matter either comes from or causes a clouded mind. Usually it's both.
Just think what happens in the mind of the person who knows the difference between restrictive and nonrestrictive clauses. Anyone who understands the distinction is on the brink of seeing the difference between simple fact and elaborative detail and may well begin to make judgments about the logic of such relationships. He may start bothering his head about the difference between things essential and accidental, a disorder that often leads to the discovery of tautologies. Furthermore, anyone who sees the difference between restrictive and nonrestrictive clauses is likely to understand why modifiers should be close to the things they modify and thus begin to develop a sense of the way in which ideas grow from one another. From that, it's not a long way to detecting non sequiturs and unstated premises and even false analogies.
Unfortunately, we just don't know how to teach skillful reading and writing without developing many undesirable and socially destructive side effects. Should we raise up a generation of literate Americans, very little of the America that we know would survive. We depend on a steady background level of ignorance and stupidity. A skillful reader, for instance, cannot be depended upon to buy this aftershave rather than some other because he is always weighing and considering statements that just weren't meant to be weighed and considered.
The next thing you know, they'll start listening very carefully to the words and sentences of the politicians, and they'll decide there isn't one of them worth voting for anywhere on the ballot. There's no knowing where this will end. (Less Than Words Can Say pp. 150-154)