Once you develop a little circle of friends, you'll largely be left alone.
So the key is to give people enough time to develop friendships - in Russia, I had the same classmates, give or take, for years. The students were separated into gradations of capacity where those who got straight As (in Russia it's a 2-5 gradation, for F-A) were put into the same class after a couple of years.
This way, smart kids end up with smart kids and those who don't do so well, end up with those who don't do so well, but then their curriculum is made a bit easier so everyone is happy.
What I experienced in Canada is that you are thrown from one set of kids to another every year and as a result, you know everyone but you don't know anyone. The 'cool' kids here were determined by looks and clothes largely because most classes were a complete waste of time.
If you made school challenging enough that those who did well were respected and those struggling, made to feel like they need to keep up and give kids enough time to get to know the same people (5+ years) - a lot of these problems would go away.
Russia is far more aggressive than Canada and violence much more common - and yet everyone I knew was ok. You come to Canada, everyone is babysat their entire lives to a point where people remain infantile in their actions and worldview - to a point where you need to implement rules of conduct in a workplace. Do you really not know how to act by the time you're 25? Should've gotten beat up a few times as a kid...