For most of the more intensive courses (100 hours and above), the teaching practice is the fundamental focus of the course, and most of the other input sessions during the course are aimed at growing your ability to 'perform' well in the classroom. This means that you leave your training with the experience of having taught real language learners, at differing levels and probably teaching different styles of class.
Distance/online courses either leave out teaching practice completely, or for some of the longer courses, require you to be observed at the end of the course by a qualified teacher-trainer. These courses are often less practical and more theoretical. Better-structured courses will include CD-roms with video of classroom teaching in action but you'll probably be longing to apply your knowledge by the end of the course. Having not been able to observe real teachers in action or feel the atmosphere of a language school, there can be more of a shock when you get into your TEFL job.
The most widely-accepted "industry standard" TEFL qualifications are the Cambridge CELTA and Trinity CertTesol. Overseas these certificates have the widest appeal, and will be mentioned the most in job ads as something like "CELTA, Trinity or equivalent".
There are many other course providers who have adapted their syllabus to meet local requirements, alternative methodologies, such as an increase in the amount of teaching practice, but who have chosen to do this without the rubber stamp and external assessment or moderation of Cambridge or Trinity and therefore fall into the category of "equivalent qualification. Beyond these substantial qualifications come a multitude of shorter, less-intensive courses that suffice to introduce the subject of TEFL, though they may hide as "certificates in TEFL". These can be anything from a weekend to one or two weeks, or if online from around 40 hours of study time.
Short courses do have a number of plusses. These are appealing as they tend to just have the best parts from the four-week courses, giving you a good insight into what it might be like to teach if you are still uncertain. They are also generally impossible to fail (intensive courses have at least a 20% failure rate). What's more, in some situations, they might be an adequate TEFL certificate for you to find work in China, and some schools guarantee paid or volunteer work on completion of a short course.
The biggest drawbacks are that it will be the lower quality schools that take on under-qualified teachers, they often pay less and offer less support, and you may not have enough of the basic techniques to make a good job of teaching and really get to enjoy it. Many of the best private language centres (universities here don’t care/understand the differences) will not hire teachers with online qualification. And if you get to your school and find it's not at all how you imagined, you may have more problems jumping ship to another school.
The short online and weekend TEFL courses start at around £200 or cheaper. Intensive courses average at about £800, although can be available for much less if you hunt around. It should be known that many ESL jobs in China are unavailable to candidates without proper certification. Also, some schools don't hire teachers who didn't have at least six-hours of observed and critiqued teaching practice on their course. Choose your TEFL course wisely!
Hope this helps,
Stuart
Photo: http://www.freedigitalphotos.net/images/view_photog.php?photogid=1913
