4YI, I grew up in the tougher suburbs of Melbourne, and went to a public school in a poor area.
I knew quite a few teenagers doing hard drugs and they got their money from crime. Robbing houses, stealing cars, robbing people at knife point. The high rise housing commission flats in Flemington turned out a number of heroin addicts. I can assure you none of those kids went to a private school. I also saw plenty of violence, including sexual violence. To suggest that public schools are fantastic and private schools are full off drug abusing, teenage perverts is just BS.
The majority of teachers at the high school I attended were next to useless, including the principal. The good teachers, few as they were, generally got the respect of even the most troublesome students.