I recently attended the Korean language learning school at Sogang University in Seoul. It lasts for about two months and is 4 hours of intense study Monday thru Friday.

I think it was really helpful. Let me give you some pros and cons.

Pros-
• excellent teachers and a "Korean only" classroom atmosphere
• If you study, you can learn a lot of Korean in two months
• excellent text books for real world conversation
• extra help classes for free covering vocab and pronunciation

Cons-
• expensive (for me it was) about 1 mil ₩
• difficult to fit in your schedule if you were teaching full time like me
• very intensive. I fell behind after the first week and never fully recovered

Overall, I would recommend it because I really learned a lot of new Korean from these classes. And I even made some good friends there in the process!