As an older teacher from America, I have grown up in, been subjected to, and witnessed the spectrum of discipline in the educational realm.
I grew up with an alcoholic father who was terribly brutal to my mother and to my brothers and me. One of the reasons I never married was my fear that I could somehow become a father like him. When I became a teacher, I realized that some children misbehave because it is their only means of getting any attention, either negative or positive. I was paddled in elementary school and in high school, and, as I look back, I deserved it, even though more positive measures could have been equally effective. But, at the time it was culturally acceptable to hit children.
However, as a teacher in America and in Korea for several years, I could never hit a child, no matter how I angry I get. That said, if a child or adult is out of control there are times when physical force (not brutality) can be the only choice. In the case of this video, there was brutality, not discipline. The teacher was angry and out of control and she physically abused the boy and abused her power and position as a teacher. The boy was already humiliated in front of his peers and the slaps and kicks did nothing positive to help the situation nor the education of the boy or the other children.
In my opinion (which granted is rather idealistic) the world has enough violence on every level, from the classroom to the battlefield, and anything we can do as teachers to eliminate the perpetuation of the mythology that power equals right, is a service to our students, to Korea and to the world. The teacher in the video had the power to hit the child, but she also had the power to teach him and the other children that there are other ways to deal with difficult situations.
Last year, a fourth grade student at my school was caught stealing at school twice. His homeroom teacher called his parents after the second incident. That day, he went home and jumped to his death from the thirteenth story window of his apartment. I constantly wonder if he was as afraid of the physical retribution of his father as I had been of mine.
I don't want my students to be afraid of me. I want them to respect me enough to not want to disappoint me and I want them to be proud of themselves when they achieve and please me. That's the only "power" a teacher should want or need.