A professional and neat appearance is very important in Korea and yet, there is no real set standard for the dress code throughout the Korean peninsula as each school may have its own particular requirements for its teachers. Some schools require teachers to dress in suits while other schools are more relaxed. In general, you must keep in mind that how you dress and present yourself dictates what people will think about you. ILE suggests that initially, teachers should overdress a little bit in order to make a good impression.
Watching how other teachers dress in your school will also help you get an idea as to what is appropriate or not in the first couple of weeks. Korean teachers usually wear conservative clothing, which cover the shoulders and come down to the knees. You’ll also notice that Korean teachers as a rule tend to dress very nice and take great care of their appearance. Do not overstress it, but take your time and make sure you find a comfortable niche.
For male teachers : collared shirts, dress shirts and sweaters with a nice pair of slacks would be ideal. Some schools may ask you to wear a tie; however, by no means are they required.
For female teachers : collared blouses, dress blouses and sweaters with a pair of slacks or a nice long knee-length skirt would be the best.
Mini-skirts, ripped or torn jean or t-shirts with offensive slogans, as with teachers in American schools, would be frowned upon and you would be sent home to change. Keep in mind that you are trying to dress in a manner which presents you as a serious teacher to your students and business directors.
People who are bigger than the average Korean (if you are taller than 6 feet) may find it more difficult to buy new clothes or shoes in Korea. You'll also want to bring shoes that are easy to take on and off.
Korea has four distinct seasons with a wide variation in temperature and a varied wardrobe is needed. Summer (June-August) is very hot and humid while winter (December-February) is cold and dry. You may want to have bulky winter items shipped to you later.
From time to time, parents of students may be invited to the school for different events and at those times, you may need to dress up more to represent your school (and yourself) well. So it will be good to bring at least one business formal suit or outfit along to Korea, as you never know what occasions may pop up. The better prepared you are, the easier you will be able to dress appropriately for any situation.