Hi Emma,

the short answer would be that CELTA is better known and more likely to get you a job. Here are the basic differences:

TKT

It stands for 'teaching knowledge test' and that's what it is basically. A written test on methodology and language awareness. It's designed mainly for English teachers who have English as a second language. The minimum level of English required to take the test is IELTS 4 (CEF B1)- about intermediate level. It's been running for about 3 years. As far as here in New Zealand, it tends to be used at the end of courses for overseas teachers of English (as an option). There is no standard curriculum for courses and people can even enter for the exam independently.

CELTA

This is a course (ie not a test) which combines practice and theory. Most places run it over 4 weeks, but it can also be done part-time. There's a syllabus which centres have to fulfill and this includes 6 hours of observed and assessed teaching practice. To get on a course, you need to pass a preinterview language task and an interview. Most candidates speak English as their first language, but this isn't a requirement. However, the language level required to enter the course is high - it isn't specified in IELTS terms, but would probably be equivalent to 7.5 (CEF C2). The course has been running in one form or another for 30 years and is very well known in the private language teaching sector in many countries.

You'll find more information at:
http://www.cambridgeesol.org/teaching/index.htm

cheers,

Martin McMorrow
New Zealand