I think it depends on the school. The one I was in was very laid back, had 2 school-within-a-school programs, which caused its own form of segregation/cliques even among upperclassmen. So I never got the unfamiliar freshie experience, but what I can say is stick to your friends from before while at the same time trying to make new ones with upperclassmen. Older kids' advice is invaluable when it comes to finding good teachers, hangouts, and other misc informational gems. Your old friends can be your support system if/when the upperclassmen reject you or troll you.