A TEFL course is designed to train teachers efficiently to work in the field of ESL and EFL. These courses are accelerated and touch on the basic principles of classroom teaching in foreign countries. Classroom courses are usually thorough and the resulting certificate is recognized in many countries (see Resources).
Online TEFL degrees, usually inexpensive and completed in 100 hours, are popular for training prospective ESL teachers in Asia. They have a similar pedagogical goal as classroom TEFL courses, but generally cost a fraction of the price and are completed in one month instead of several. The downside to these courses is that they are not accepted in as many countries. South Korea is a country where an online TEFL course certification is acceptable and gains you a salary increase over non-certified teachers.
CELTA courses gear toward training ESL teachers how to teach English to adults. There is not much emphasis on childhood ESL education. CELTA courses are widely recognized worldwide, are considered more thorough and are generally more expensive than TEFL courses. CELTA courses are usually completed in a classroom instead of online, since they usually include live experience and practice.
Regular teaching credentials are most common for teaching within the United States, usually in a specific state since credentials are mostly state-specific. Credentialing programs are usually one to two years in length and costs are usually average for higher education degrees. There is no specific teaching credential for ESL, however a credential in a subject like English with an emphasis on the art and science of teaching may suffice for ESL teaching. Recent demand for ESL teachers has increased pressure for institutions to offer specific credentialing programs for domestic adult ESL teaching.