I was in a store yesterday and I noticed the clerk (a young, college-age woman) was studying some rather difficult looking material, with a notebook open to a set of handwritten notes on what looked like a medical topic. The notes were completely in English, with lots of long words and full sentences, hand-drawn diagrams and charts, all with a neat, miniature penmanship. Yet she saw me and failed to produce an English sentence, although she clearly wanted to.
I was struck by the realization (a realization I've had before, too) that although most Koreans exit their primary and secondary school systems still unable to speak English, despite a decade of obligatory English class, nevertheless many do manage to acquire a substantial level of skill in reading and writing.
And then this morning, I found a comment by a Korean (well, I assume the person is Korean, since the screenname used for the comment is "The Korean") on a blog post on problems with English education in Japan and Korea by a blogger named "chrisinsouthkorea." The comment is worth quoting in its entirety (moreso than the original blog post, which basically says the same thing a thousand vaguely disgruntled foreign teachers on a thousand blogs have said about English education in Korea). It's quite insightful and worth seeing for anyone teaching English in Korea.
I would suggest that English test should be strongly focused on reading and writing. (Maybe you included these concepts in "comprehension ability.") But my main point is that speaking is a really overrated ability. And a part of the reason why it is so overrated is because (I trust you won't misunderstand my intention when I say this) NSETs [Native Speaker English Teachers] tend to focus on their own frustration with being unable to communicate with their students such that they overlook what their students are halfway good at.
I don't [think] NSETs really get to see the practical application of all that English education in Korea. Broadly speaking, (of course this could differ individually,) Korean people learn English so that they can work at a company that deals with foreign clients. After all, Korea is one of the most export-dependent country in the world. They do NOT learn English to make small talks with Anglophones. In this context, reading and writing with high-level vocabulary and grammatical structure is the most critical skill to learn, not speaking.
There's another point, worth adding: reading and writing skills are much easier for non-preschool-age humans to acquire than speaking skills. Witness my own substantially better competence with written Korean over spoken Korean, or consider the fact that although I can enjoy reading a novel in French, for example, I'd be hard pressed to have even a basic-level conversation in the language. And although I can get the gist of a newspaper article in Dutch, I don't even know how to say "hello."