I did Extension English in Year 11. It was definitely my one 'bludge' unit; all my assessment tasks (incl. prelims, didn't prepare essay or creative) were in the 80-85% range, and done at the last minute. Given everything else you have to go through & complete in year 11, the subject is taxing, and you will for sure find yourself overlooking it - especially around your exam period.
Extension English aims to extend your understanding of a text (or myth/idea) by considering context -- i.e. written around WWI, very pessimistic and droll. The best way to describe it would be this: in normal (advanced or yr. 10) classes, you may have had sophisticated, intertwining ideas that were interesting, but not realistic to place into any body of work. A higher word count in Extension means (with many revisions) you may be able to discuss these ideas in your critical & creative works. This is not to say that you need sophistication to do well. Anyone that's done senior English will tell you dismantle that myth.Those that did best in the course (we had two classes) achieved mastery over the fundamentals, being able to deliver a near-flawless, relatively forumlaic response that displayed not only their passion for the topic, but also the many hours spent researching & interlinking their ideas. These skills are built over the course of the year through the various responses your teacher may prescribe.
Anyways, I dropped it for 4u math
Good luck on your endeavours.