Not to mention a school's ranking has
no bearing on what rank an individual can achieve who is attending that school. You hear about kids who went to TAFE for their HSC achieving ranks of >99.00.
A poor ranking of a school simply means that perhaps the assessments the school administered to students were too easy and inadequate preparation for the Higher School Certificate external assessment (major works and examinations). The HSC external assessment is worth 50% of your final HSC mark and is what is used to moderate (change for no good reason) your marks. A poor examination mark in most cases means a poor HSC mark and hence, students of schools with easy assessments (poorly ranked schools) sometimes bomb out and keep the school's ranking low.
Neg rep me if this is bad advice, but I am just paraphrasing a post you made several months ago, Anna. I do listen to you after all.