So just to summarise what has been said, and to add a couple of points of my own. A SAC is School Assessed Criteria. Your SACs and the final exam are the ONLY things that go towards your final study score. If you look on the VCAA website, it will show you what the percentage of your mark each SAC relates to. Unit 3/4 SACs are the only things used to make up your cohort ranking, and that ranking is then used to scale final exam marks. Your tests, and non-SAC assignments can be made a required task by the teacher, that you need to pass those tests to get an S, but they do not count towards your mark. They are generally used to give the teacher an idea of where you are at and if there is anything that needs improving on, and also to give you some experience. But SACs and the exams are the important thing. Another thing, SACs are only important as far as getting your S in Year 11, but in Year 12 your mark counts!