Why, you're absolutely right. Prior to completing HSC English I would not have been able to type this post.
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Seriously though, it is useful for what it does, it just doesn't do the right thing. Firstly we need to accept that no matter what the course content is, at least 60 - 90% of students won't care and will treat it with the same level of apathy whether it's old-school grammar or extreme post-modern garbage. Remember that the English language was still constantly changing in the days when grammar was taught.
Now, the chances of a return to the older style of teaching English is quite impossible within this generation. As you may know there is currently the trend of the people "In Charge" having to periodically introduce new, trendy ways of teaching to make sure it appears to voting parents that they're "Doing Something (tm)". Add to that the groupthink so prevalent in all humanities-type fields in university and there's no surprise it's filtered down to high-school level.
Remember most kids don't care and as far as they're concerned, all school is useless be it maths, English or otherwise. In my opinion the content of high school English coures is NOT the major factor influencing the evolution of our language.
As for the current English Advanced course itself, it's useless. Even those that enjoy Extension 1 and 2 English courses generally (based on observations of dozens of threads like this on BoS) hate the advanced course too. It does not teach us "how to communicate" or any such nonsense. It teaches us to read a selection of "texts" (because an advertisement has as much value as Shakespeare now) and to write down all the "Right Ideas" about them in a series of forty minute essays. Nothing more, nothing less.