For many k-12 jobs abroad, the TESOL certificate is a requirement. In programs such as EPIK or JET, you do not need a teaching license or a degree in Education. A university degree in any area and a TESOL certification are enough to get the job.
In most programs abroad, you will be hired as an ESL teacher, so the TESOL course is crucial for the job. Even if you do not have any previous teaching experience, the TESOL course will give you the skills that you need to plan and deliver effective ESL lessons using communicative activities and authentic materials that supplement the textbook.
For some k-12 jobs abroad, such as ADEC in the United Arab Emirates and NETs in Hong Kong, you will likely be hired to teach the standard curriculum in the English language. As is the case with k-12 teachers in North America, you may be teaching to a cohort of students whose level of English is very low. Some teachers even experience the added challenge of teaching in places where there are cultural frictions when it comes to the use of the English language. The TESOL course will help you communicate better with your students as you plan more meaningful lessons.