This is an interesting thread, but I would interject that in a hagwon atmosphere you get those few students that are forced to level up to intermediate even though they do not have any of the basics down. I am sorry, but for the sake of understanding and comprehension, I think Korean should be used when it is something in relations to grammar or perhaps a jargonated word that is hard to explain in English. Seriously you can't pantomime every word in the English language. Also, phonics children are much more manageable if you know Korean. With advance students, I take a communicative approach and JUST use English. Also I forbid all my students to speak in Korean in class unless absolutely necessary. It seems to be highly effective that way and most of my students legitimately level up.
But seriously, what's more effective: knowing the Korean and giving the translation to them right away or doing a 5 minute song and dance over one phrase when it is not necessary going to translate well and you have a rigid schedule to adhere to? On that note, I think about absolute Konglophiles (Korean teachers included) should stop teaching ESL, but that will be a cold day in hell.
