Before arriving in Bangkok I studied some basic Thai using the Pimsleur Thai audio books, this language system was developed by the US army for teaching troops basic language skills in a variety of languages. The Thai one is amazing, there’s no writing involved and you don’t even really have to actively try to remember things, you simply listen and their use of repetition allows you to almost automatically remember things. I’d definitely recommend to anyone visiting Thailand for any length of time.
When I arrived in Bangkok, I wanted to build on the basic Thai I had learnt from Pimsleur and get up to a half decent convocation standard. After a lot of shopping about and a few trial lessons from different schools I decided to go with Everyday Thai School in Chong Nonsi. They offer everything from one off private lessons to intensive 60 hour group courses. All the teachers were pretty good and the course content is up to date and relevant to everyday life. After two intensive 60 hours courses, which took a total of 6 weeks I’ve found I have built up a good vocabulary and can hold a half decent conversation, as well as having made a decent start on being able to read and write.
The price for the group course is excellent value at 7,000 baht (£140/$225) for 60 hours, it works out at about 116 baht (£2.30/$3.70) per lesson, this also includes all your books. Check out what they offer at http://www.everyday-thai.com or contact them at firstname.lastname@example.org