Like most teachers, I have heard again and again that teaching grammar makes no significant difference in a student’s ability to write grammatically. That’s just never set well with me.
One of the primary issues seems to be that grammar is taught as content to be learned rather than a skill to be internalized. When a student learns that a noun is a person place or thing, he quickly forgets this because it is information that is not reinforced. Knowing the parts of speech is simply not a useful knowledge because it is not put to work any more than much of the content a student might learn during a history lesson.
Grammar can be learned better if the structures of it are practiced in much the same way other skills are practiced, such as a musical instrument. A boring as it may sound completing exercises on grammatical principles would ensure that students internalize the core idea.
To make grammar more meaningful and more memorable, it needs to be put to use in developing a writing style. When students can see how it is used by other writers and how it can be used by them to create certain effects in writing, they are more likely to hold onto what they have learned and put it to use in their own writing.