TL;DR - Really smart students are completing a subject’s course early, then choosing a harder subject which makes their other mark irrelevant. Due to the system we have, this means that other students in their school are given their really high marks, even if they did shit, meaning that everyone else competing against them has a much worse time.
So, in New South Wales, Australia, in the final year of school (Year 12), every student completes what is known as the Higher School Certificate (HSC). You pick which subjects you want to study for those years, and complete assessments and exams as normal. After all your exams are completed, you’re given a ‘mark’ called an ATAR, which is essentially a rank against every other student in the state. A student's final result is divided up: 50% of the final mark comes from your marks in school-based assessments, and 50% comes from the final exam. Your ATAR is then used to get into universities; for example, a course in Engineering might have a minimum ATAR of 85; therefore, you have to beat 85% of the students in the state to get into those courses.
When choosing a maths subject, there are 4 tiers (in ascending difficulty): General, Advanced, Extension 1, and Extension 2. Both General and Advanced Maths are worth 2 ‘units’ - each unit means that a minimum of 50 hours must be spent in class learning the course work. Extension 1 and Extension 2 are only 1 unit subjects.
Now, to do Extension 2, a student must also do Extension 1 and Advanced Maths. Doing Extension 2 means a combined minimum time of 200 in-class hours to complete all the coursework. However, due to the difficulty of the Ext. 2 course, if a student chooses to take Extension 2 Maths, then they will not have to complete the Advanced Maths test, and the unit values for both Extension 1 and Extension 2 are adjusted so that each one is now worth 2 units.
Another quirk about this system that needs to be noted is that a student’s performance in the school-based assessments will determine which result a student will get after completing their final exam. For example, if Student 1 gets a higher ranking in school-based assessments than Student 2, but Student 2 scores higher in the final exam, then Student 1 will be given Student 2’s exam mark, despite performing poorer (ignoring extreme outliers). Now, that’s bullshit in itself, but it gets worse.
In certain selective schools, mostly in Sydney, really smart students are being “accelerated”, and are completing the Advanced Maths course in Years 10 and 11 (the third- and second-last years of school), instead of the last 2 years. This means that, if they choose to do Extension 2 maths, there is a mark (usually a ridiculously high mark) that cannot be assigned to that person, because they haven’t actually completed the Advanced Maths course.
Remember how I said that the best-performing students in the school-based assessments are given the highest marks in the final exam? Well, because of these really smart kids getting these high Advanced Maths marks, and then not using them, those marks are then given to the people who have actually completed the Advanced Maths course as a subject. As a result, the lowest marks from these students are simply discarded, which makes the entire group of students have crazy high marks overall, even if some of them did really badly.
Due to entire year groups from these schools having really high marks, they usually rank very highly when compared to the rest of the state. As a result, any other schools that aren’t selective are screwed, because they have students who get much lower marks, which brings the whole group of students from those schools down, even if some of them did really well. Thus, some students could be given a really high ATAR, even if they’re really bad at it, which pushes the rest of the students in the state further down the rankings, resulting in a lower ATAR, which makes it much harder to get into university courses.
Yup. I'm fucked.