my middle school went up to grade 9, so mostly everyone stayed at that school.
but the highschool also had grade 9, I left early and lost all my old friends. diding care much since now I have much better friends, and a large number of people at that school sucked ass and did way to many drugs.
id say it depends on how big the school is, if its small anough, even not being in any of the same classes shouldint split you up.
I was only in one class with my best friend, and we are still best friends.