How does what school you go to affect your ATAR?

Okay so I consider myself to be an academic student, but I go to a public school ranked very low in the state. (it's only been open 6 years). I've heard something about that if you go to a private school or a school ranked higher in the state, your SAC marks are scaled up more than if you go to a less academic school. Is this true? If it is, how much of an impact does it have on your score? Is it a big impact? It's really important to me that I achieve a decent score at the end of year 12, (I'm aiming for 95.00), do think this is possible at the school I am currently attending?