Qualifications for Teaching in Thailand
In most cases, you must have a bachelor's degree to teach English in Thailand. It doesn't matter what subject it is in, just be sure to bring several copies of your diploma as proof, and diploma copies of any other degrees you may have. TESL certification from RSA/Cambridge or CTEFLA programs is not necessary, but will ensure a higher salary at commercial language chain schools such as ELS International and ECC.
In general, you do not need to be a grammar expert, but commercial language schools will require you to take a grammar test, so it doesn't hurt to brush up on basic tenses and structures.
The demand is mostly for conversational English, especially for business and tourism in Bangkok, Chiang Mai, and other areas that attract international trade and visitors. Most Thai students have been schooled in British English, but with the advent of capitalism and Western consumerism, many Thais prefer to learn American English over British or Australian English.
Thai students are false beginners - they study reading, writing, and grammar for years but have a limited ability to speak and understand English. The problem, as with most Asian countries, is exposure to native speakers. Thailand is a homogeneous nation with Thai as the dominant language, so there is little incentive for daily English usage.
Overall, the two most important factors in hiring to Teach in Thailand are availability and teaching experience. Saturday is considered a working day at some schools, at least a half day from 8 or 9 a.m. until noon or 1 p.m. Many schools also have evening classes.