OK this is how it was explained to me.
The HSC mark you get, is the HSC mark you get, regardless of anything else you do. They take those raw marks and scale them so that there is a bell curve over the scaled mean (it was 60% in my time, 50% befor that).
You do school assesments and gain a school ranking. These marks and ranking are sent into the BOS.
Now imagine these school assessment marks and rankings are written onto a piece of elastic. Say the top assessment mark was 90% and the bottom 35%. And everyone in between is there, too.
NOW, after the HSC is done, the TOP mark for the cohort is where the top of the elastic is anchored and the BOTTOM mark for the cohort is where the bottom of the elastic is anchored. Every mark in between is adjusted according to where the elastic stretches.
If the TOP HSC scaled mark is HIGHER than the assessment mark for the top ranked person, then everyone's marks above average are pulled up.
If the BOTTOM HSC scaled mark is LOWER than the assessment mark for the bottom ranked person, then everyone's marks below average are pulled down.
SO, if the top ranked person only gets, say, 75% in the HSC, but the top HSC cohort mark was 99%, they will get 75% for the HSC mark and 99% for the assessment mark.
If the person who achieved the top HSC mark of 99% was only ranked, say, 4th (with a mark of 79%), and that mark was stretched to 84%, then they get 99% for the HSC and 84% for the Assessment.
SO, what is the lesson here? EVERYONE is a year cohort should work TOGETHER to ensure that the ENTIRE school group does the best they can possibly do. Stop competing against each other and start working against the system and try and beat it by everyone getting Band 6!!!