If it was one teacher, fair enough, but it was nearly all of them, and protracted over a five year period. I asked to change forms, but told no space available in other forms. The teachers just didn't take it seriously, even when I showed them bruises, torn books, damaged bag, etc. I also got the usual brain dead comments of "ignore them" (difficult when they're burning you with a fag end), or you must be doing something to antagonise them, etc - i.e. the usual victim blaming.
But "harmless messing around" becomes damaging when it's one sided, repeated, ongoing, etc. Where do you draw the line? I'm sure that vast majority of bullies thought they were just harmlessly messing around, but I'm sure that's not how it feels to those on the receiving end all the time!