((For clarification: I am a geek, not a dork or nerd.))
Do you know why Americans are accused of knowing less grammar than the rest of the developed world? No, it's not because the Brits are a bunch of stuck-up meanies. It is because we don't actually learn any grammar past elementary school.
Oh, we learned have "grammar lessons" of course, but we don't learn any grammar, because grammar means knowing how to speak and write well, "well" being judged according to a set of rules. All we learn in class is what all those words are called--prepositional phrases, infinitive forms. I shudder to think I saying "when will we ever have a use for knowing that in real life?" because when someone says that, 99% of the time there is a perfectly good reason that the person doesn't realize.  The reason is to make learning grammar clearer, because it would be fairly confusing for someone to tell you to always put a comma after a prepositional phrase at the beginning of a sentence when you don't know what a prepositional phrase is and think you're talking about apostrophes.  Problem is--we don't actually use what we learn in grammar, because we don't learn grammar!
Maybe it's just my school. In sixth grade, I attended a school in California and my teacher was the fabulous [name removed, henceforth known as "Edna"]. At the beginning of every grammar period she would put a sentence on the board and we would have to correct it. In that way, we learned to put the periods at the end of sentences, where apostraphes should go, not to say "like" or Edna would slap you, etc. Now that I look back on it, it's very basic stuff I learned in third grade--I had to figure out how to use an ellipsis all by myself. When I move to New Jersey, the teachers did not do that, even though the new school was actually a better one.
Every time my teacher (who is not fabulous) takes out the grammar book, I moan and groan like everyone else in the class. But if she would just teach us some frikkin' grammar, I would jump for joy.
 Speaking of perfectly good reasons--I have doing anything if it's not for a good reason, so every time I use a grammar rule I think of a reason for it. Guess what? You actually really do need grammar for many good reasons! Like, OMG! So, bring it on--tell me any rule, any rule at all, and I will tell you why it's needed. Seriously, please do. I am a geek, bordering on nerdiness.
 And, of course, because the teacher would get fired if she didn't teach what was in the basic curriculum.