SAC scaling is quite a tricky and complicated process. Here’s a video I found that gives a great summary (full credits to Julian). https://www.youtube.com/watch?v=h9KgF3-8d84

More detailed information can be found from the VCAA website: http://www.vcaa.vic.edu.au/Pages/vce/exams/statisticalmoderation/statmod.aspx

If you’re at a school with a strong cohort, SAC scaling can often benefit you because your SACs get ‘lifted’ by the performance of your class. This is assuming that your cohort does well on the final year exam, and at top schools this is the norm.

If you’re at a school with a not as strong cohort, SAC scaling can potentially be harmful to your study score and hence overall ATAR if you are somewhere near the ‘middle’ of the class. If you’re aiming for a ‘perfect’ 50 raw in a subject, then it is quite imperative that you are near the top-ranked students in the cohort since a 50 raw often requires you to have perfect scaled SAC marks.

If SAC scaling still doesn’t make sense to you after watching the video and reading the link, then my advice would be just to aim to be top ranked in your subject at school and the rest will sort itself out.