That is correct.
If you are ranked first internally, you will get the highest external mark (as your school mark) even if during the year, you were scoring say in the 50s
Just because you are scoring in the 50s but you are coming first, that does not mean marks are not important.
The rank is definitely more important . It determines how you will be scaled .
Though you should be aiming to get a high mark in all your exams and assessments .
No it does not. Your marks are moderated, not your rank. Your marks are moderated based on your cohort's HSC exam marks. The bounds of the moderated marks are the highest and lowest HSC exam marks, so at no stage does BOS say 'you are ranked 8th, so let's give you this mark'.
Actual mark may be not a good representation, ie assessments/trials may have been hard.
In terms of ranking, for example
School rankings:
1) John
2) Bob
3) Sam
4) Tim
Say you were Bob, 50% of your mark for a course is acquired through the 2nd highest mark achieved from the HSC exam by your school, the other 50% is what you score yourself.
That is wrong, and a common misconception. Bob does not receive the second highest HSC exam mark of the cohort. He is moderated based on his school mark and how well the cohort performs as a whole, never by his rank.
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Marks are definitely more important than ranks, but in a certain context. The mark itself, has no meaning. It's where your mark is positioned relative to the cohort which matters, but this does not mean the 'rank' of the student. Coming 20th by 2% puts you in a better position than coming 20th by 20%, yet in both cases, you are the same rank, so clearly ranks do not matter. The only cases where ranks do matter is if you are first or last. In these cases, the first ranked student's moderated assessment mark will be the highest HSC exam mark of any student in the cohort, and vice-versa for the last ranked student. Everyone else in between is moderated based on how well they performed in the year in terms of how close they are to first place, in terms of marks, not ranks.
BOS takes into account the relative gaps between students. If you are not first, then you need to ensure you have as many marks as possible, otherwise factors such as a poor tail or a poor mean of marks can distance yourself from the higher end of marks. Being ranked 2nd won't help you if you are quite distant from first place, and your cohort is stretched in the HSC exams.
As said/implied above, you may be achieving 90% or whatever, and end up getting a low HSC mark of say 80. This is because the standard at which your school sets assessments is not to the standard of the HSC. The problem is that many students only know how well they perform relative to their school's standards, so they are conned into thinking they are set for the HSC and end up doing really crap. This is in no way linked to how well you rank at school, so associating the two in this context is erroneous.
But the important point is to ensure you know how well you are performing relative to the standards of the state. If you feel as if you are not being tested, or the marking seems to be easy (no matter how nice it is to get 95%), then chances are your school isn't setting assessments to the standard of the state. But at the same time, if you aren't doing too well, but it seems like the content isn't too hard, then chances are your school isn't effectively teaching you to a standard that is competitive at state level. Both are hard to tell when you are in the middle of it, so a good way is to do past HSC papers and see how you perform, get someone from BoS or another school to mark it etc. Doing past papers from other schools (preferably selective schools since they are rarely below the standard of the state in most subjects) is also a good way of getting a variety of questions.
To quantify which is more important when one is dependent on the other makes no sense. Marks determine ranks, ranks do not determine marks. BOS does not allocate marks to certain ranks, except first and last, but those marks are based on HSC exam marks which are independent of ranks.