Earlier quoted context omitted.
I would take it 1 step farther, if you're not teaching your children how to deal with bullies themselves then you're harming them for life. There's a point at which the child cannot possibly deal with it and you as the parent must step in to protect them, but most of the time if a child learns how to deal with bullies you don't need to.
What would you suggest to teach them? I was never really bullied but worry now about my own son and what to do if he is.
Outside of that, they need to be taught that buttholes exist and dealing with them is a fact of life. They shouldn't start things, but they definitely should end them. That was the metric for us while in school, especially if we got into "fisticuffs".
I think for you it's important to understand that school and teachers can't be trusted. I'm not saying teachers suck, but shitty teachers exist. My middle brother once had a teacher take a dislike to him because he corrected her in class. I once had a teacher that would make me stand out in the hall behind the coats on the coat rack. My mother showed up at the school for both, I was pulled from that class and put into another class with a teacher named Mrs Parker, whom I absolutely adored. I still remember the song we would sing at the beginning of class (about parking cars).
My point is that if your child is having an issue with a teacher, don't assume it's the child, my experience is that it very often wasn't. You build trust with your children by SHOWING them that you're there for them. Of course, that doesn't mean every poor interaction with a teacher is the teachers fault. We were dirt poor so I suspect that had something to do with it as well.
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Anyways, none of that is really concrete, I don't know that concrete advice really applies to a question like that. Imo, kids learn what you teach them even if you don't know you're teaching them, and there is no such thing as a single glorifying lesson, it's a slow march over time, exactly as you would do to build trust with someone.