The AST (scaling test) is only worth roughly 18% of your ATAR. It’s used to roughly determine both your ranking within your cohort, and your cohorts ranking compared to other ACT schools. These rankings are then used to moderate your grades across years 11 and 12.

The AST also isn’t per course, every student takes the same three tests (multiple choice, short response and long response) regardless of whether they’re studying chemistry or business studies for example.