How does your school or cohort affect your HSC

[lsam]

 I recently moved school in year 11 from a public school to private school. The teachers int he new school are ok while most are the same level as those in my old school where i had good teachers for all my subjects. I moved because of the cohort since in my old school some of them didn't care and I thought they would bring me down while at the new school everyone is determined to study well. I know that i could get at least in the top 10 for most or all my subjects at my old school while I would most likely be in the middle or towards top in the new school. My subjects are the same in both school except I have to do religion 1 in the private school since it is compulsory. My subjects are 1. Ancient history, 2. Advanced and extension maths(most likely going to drop extension), 3. Advanced english, 4. PDHPE, 5. Visual Arts, 6. Biology 7. Religion 1 in new school. I was doing accelerated biology at my old school but cant do it in the new school. My old school was ranked around bottom 200's while the new school is top 150. I just want to know how my grade and school affects my ATAR and any reccomendations on what to do.