Fighting back is specifically not playing along. It's imposing your will over yourself in place of the bully's. Not fighting back, telling the teacher, a parent whatever is playing along to the bully.

Humans are pack animals with a social order. By suggesting your child escalate confrontation out of the pack at all times, you have ensured that the bully remains their superior to them when the higher authority is not there.

There WILL come a time in life when your child has no higher authority to appeal to. If they aren't able to establish their own place in whatever pack they are in, it will be established for them, possibly in ways that are not in their own self interests.