FAQ:

A large number of overseas private language schools hire teachers on an as-needed basis any time of the year. Often, they are willing to hire you immediately to replace a teacher who has just left or a teacher who is about to complete their contract. Most of these contracts are for a minimum of one year. Our Job Placement Service has numerous job openings year-round and assists our graduates in finding teaching positions every month of the year.
Private language schools which run summer programs tend to hire in the late spring which is ideal for university students looking to work right away. Many summer camps only last a few months and thus involve short-term contracts between May and August.
Government programs such as JET (Japan), EPIK (Korea) and NET SCHEME (Hong Kong) hire a few months before the academic year starts. Keep in mind that public schools, colleges and universities generally begin in September (Northern Hemisphere) and in March (Southern Hemisphere).