I love this drama for many reasons, one of them is this cute little girl, Kazumi!
However, if the story is taken seriously, it conveys a wrong, in fact, dangerous message. The teacher basically becomes a big bully to teach kids how to deal with bullies. She does all terrible things to her students, making an atmosphere in her class that encourages bullying. And when a student is bullied by her classmates, she does nothing with the excuse that if she does anything, it just makes the situation worse. Bullies are free to do whatever they want and all the pressure and blame is on bullied kids to do something.
So, the whole idea is to make the situation for these 12-year-old kids so horrible that makes them do something about it. Maybe this was the traditional teaching method in the far past, but now, it's more for psychopaths. I hope no one takes this aspect of the drama seriously.
To be fair, as said, there are many good things about the drama. Especially, I really enjoyed the sisterhood between Kazumi and her older sister. I really wish I'd had such a sister!
To summarize, it's highly recommended to watch, but not as a serious stuff on teaching methods!