You do a subject and get sac scores. When you complete all your sacs for the year your teacher will add them up and rank you according to how well you did compared to everyone else in your school in that particular subject. Rank 1 means you got the highest sac total at your school and your teachers will eventually have everyone ranked. This information gets sent to VCAA eventually. You do the exam and VCAA get some examiners to mark it. They then change the sac marks from your school according to how everyone performed on the exam. Rank x gets the x highest exam score. Example might be rank 1 at your school bombs out and gets an E. If the highest exam score was an A+, they would get A+ sacs and an E for the exam. The reason this happens is because different schools set different sacs. Some schools set easy sacs and students can get very high marks. Other schools might set difficult sacs and the students might not get marks as high in comparison. Come exam time, the school with the difficult sacs will most likely perform better and their sacs get moderated so they reflect the exam performance. The school with the easy sacs might perform average, so their sacs might scale down to reflect their exam performance. Scaling is just a process to make the playing field fair, so that is how your cohort can affect you. The only people who don't get affected by the performance of the cohort are the people who are ranked first. So to really answer your question, if you get a bad ranking in a weak cohort you might be in a bit of strife as your sacs will most likely scale down as it is expected that your cohort will perform poorly on the exam. Of course this isn't always the case as your cohort might get spectacular exam results which in effect, bump up your sacs marks. Getting a bad ranking in a strong cohort will not be as bad because their sacs will most likely scale up.