It was actually my Korean co-teacher that introduced my to Power Teaching and I LOVE it!! I worked at a hagwon for a year, and I only wish I knew about this method then!
At my main school, I only teach 6th grade, and this method works well for them. I saw some people were worried about that, but actually, it is wonderful! At my country school, I have 3rd through 6th grade, and I have implemented this system there as well!
The ones we use are:
Class-Yes (to get the class's attention during activities or rowdy times...with varying clapping patterns and tones of voice)
Teacher-Ok / Switch-Ok (for practicing new sentences and dialog...mostly for Listen & Repeat and Look & Speak)
Hands & Eyes (this doesn't work as well as the others, but sometimes we use it)
We also do a few other reply commands with the teachers and students:
Are you ready? / Yes, I'm ready!
Everybody, TV. / Look at the TV.
Got it? / Got it.
Look, look, look at me. / Look, look, look at Teacher.
I really enjoy this method. It helps to end the shouting that some teachers think they have to do (I was one of those at the hagwon). It also keeps the students involved and keeps their attention.
Good luck!