Our school system has a "zero tolerance" policy that suspends both students who were in a fight. A child of mine was once standing in a schoolyard when someone ran up from the side and knocked him over, then started hitting him while he was down. He did not hit back. They were both suspended. That is what "zero tolerance" gets us.
That child was already in martial arts, and in fact "not realizing someone running up to me from the side is actually attacking me" became a discussion point in that week's lesson. What had already been covered in detail was how to avoid fights. Oh, how the older children loved acting out the chest-puffing, arm-waving, you-talkin-to-ME of a young man working up to a fight! In general, the training did work to prevent fights, to make them shorter if they started (the only thing better than a two-punch fight is a no-punch fight), and to reduce the chances my child was hurt in anything that did start.
When it comes to teaching your own child how to fight back I suggest one of these three:
- "never fight back, never hit anyone even if they hit you. Run away, yell for help, cover your head, but never ever hit anyone." This may help keep a child out of trouble in a non zero tolerance school, and may fit your own philosophy better.
- the advice you were given - no holds barred, they started it, you finish it
- for anything more subtle, get someone who teaches fighting to make the subtle distinctions and teach the techniques, including spotting these things brewing. I think it's a very hard thing for parents to teach because we love our kids, don't want them to get hurt, don't like imagining bad situations, and either assume other kids are just like ours or other kids are all evil. Instructors of boxing, karate, kung fu, judo etc are freer to explore what-ifs.
I grew up in a time when teachers thought fighting was fine, and hated it. Today's world is better, but more complicated.