I know this is a relatively old thread, but I am new here and totally agree with you that teachers didn't care one iota who started the fight, both (or all) parties were punished irrespective of guilt. In my school that invariably meant a caning. In my case I only got caned for fighting once, and it was the only wholly unfair punishment I got.
For all my other faults, I was the ultimate peacemaker. This really seemed to nark the class bully. One day - I was 12 -he literally started punching and shoving me for no other reason than I was 100% different from him. I defended myself, but don't think I even knew how to throw a punch. But the usual circle of cheering boys surrounded us, and that deemed it a fight.
Prefects separated us. No questions were asked. We were taken to the deputy Principal's office. Again, no opportunity to explain -merely lectured - very briefly - on the evils of fisticuffs (sic!) before being ordered to bend over and given six really of the best on our bottoms.
But even though it was grossly unfair, I don't remember especially resenting it, but more taking it as a part of a 1950's schoolboy life. You win some, you lose some. My two consolations? I took my caning a lot more stoically than the bully. And a year later he was expelled. For bullying!