I agree with everyone here about talking to the teacher and I also want to echo that what was said by the teacher may or may not have been exactly what your DD perceived. I have no doubt that your DD told you exactly what she thought was the truth. And it may be the truth. But it may also be a misunderstanding. I run into this all the time with my patients. They come in telling me that "The Dr. said I was supposed to do X." They are almost always absolutely certain that's what they were told. If it doesn't make sense, I always check back with the doc and invariably the patient was told something that they misunderstood to be something else.
So I would approach it that way by saying something like "I know that very often kids can misunderstand instructions and I wanted to clarify something. DD came home the other day and told me X. I was surprised because it didn't strike me as a method of dealing with bullying that would be encouraged so I wanted to make sure that she is dealing with these other girls' behaviour appropriately. And BTW, what is your policy/approach to bullying?"
It can also be very helpful in these situations to say something complimentary to the person you're talking to before you get to the meat of things. It helps to keep people from automatically getting their hackles up. Once that happens, the person won't hear a word of what you are saying and will just be on the defensive.
Communication can be very tricky sometimes. Good luck.
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