OP - Different kids respond differently to discipline, as I am sure you are aware. My son doesn't look concerned when I look him in the eye and speak very firmly, he yells in my face and hits me and keeps doing whatever he was doing. Its very difficult having a defiant child who doesn't respond like other kids to discipline, and I think the mother is likely to be offended if you approach her and suggest different ways of discipline. I don't think there is much you can do, particularly because you said she DOES try to deal with the behaviour. If she sat back and was too busy chatting to know what her child was like then I would agree that some gentle way of broaching it with her would be ok.
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