1 - Conversation: Why should YOU teach it?
Reason one: Only you can! Look around your school and you can probably count on one finger the number of people who can hold a recognizable and worthwhile conversation in English. Thai and Filipino (and French!) teachers can probably teach the dull stuff like grammar and writing better than you can, but only you can speak English like a native.
Reason two: It matters. More than any other aspect of English language learning, actually speaking the language is the most important. We speak a lot more than we read and write, don't we? It's the most basic, most common and most important of human interactions.
Reason three: It's rewarding... for them, not you! I think it's fair to say that most Thai students at any level, rate their English language ability in terms of how well they can speak the language rather than, say, how many irregular verbs they can reel off.
Students find the ability to be understood in a foreign language the most gratifying aspect of the pain of learning it. If they don't get an opportunity to speak in the classroom they'll soon get bored. On the other hand, if done in an interesting and inclusive way, performing meaningful dialogs in class can be fun and rewarding.
Reason four: It's easy! You want to make your life easier, right? I do, and yet I see many native English speaking teachers spend most of their time on reading and writing practice. Many of them just abandon the more important speaking and listening skills that students need and which only they can teach.
Leave the boring stuff to the non-native teachers. They can probably teach joined-up-writing better than you can anyway. In my view, if you're NOT teaching conversation skills, you're a waste of an expensive resource at your school.
2 - My students are all deaf mutes!
Traditionally in a Thai school, lessons are delivered and at the end of the hour, the teacher considers them learned and that unit is closed until the test... where it's inevitably revealed that nothing was learned at all! This applies to most of the subjects they are taught... including their English classes.
This means that your students are mostly passive receptors of information rather than active participants of your class. It's not your fault - it's just the way things are in Thailand.
Obviously, this isn't going to work in a conversation class which requires everyone to make a noise and get involved. So you have to make some changes that go against the grain of the traditional Thai classroom setting.
If your classes are ‘routine driven' then Thai kids will open up more readily. (‘Routine driven' is not the same as boring!) If your students are comfortable around you and know a little bit of what to expect, this helps a lot.
There are a couple of other things you can do, too. Re-arrange the desks, maybe...have a shouting competition at the start of the class... (brilliant fun!) Have the dialog you are going to practice on the board/screen ahead of time to give the kids a heads up on what they'll be doing...
But there may be other reasons why your classes are quiet which could be symptomatic of more serious issues. The assistant teacher could be very strict and not allow your students to ‘let go' in the class. You may be practicing conversation dialogs that are too difficult or simply irrelevant to your students.
It could be you! Are you speaking too fast or using words and phrases like ‘So...', or ‘OK, then!' in the classroom? If you are, stop it. They are distracting and meaningless. Filling the silence with noise is a big mistake. Most teachers do this and it's very confusing and off-putting for Thai students to deal with. Also, speak clearly and slowly and always face the class when you do it.
3 - Let's get talking...
A big part of teaching conversation is getting your classes to understand that conversation classes are NOT reading classes. They can (presumably) already read, right? So, questions have to sound like questions and answers have to sound like answers. This takes your students a lot of getting used to and this aspect of teaching conversation will be the one that taxes your patience more than any other.
Another mistake (in my view) is pair work. This almost always leads to students just chatting in their own language or just making a balls-up of the pronunciation when they are out of the teacher's attention range. It may kill some class time for you but it rarely does any good as far as learning conversation is concerned. Lots of teachers disagree with me but they're all wrong! :)
Of course, talking is also about listening. You can't carry on a conversation without listening to your partner! Even in large classes, you can teach conversations effectively. Pairs stand up and recite a dialog and the class listens and you intervene and correct as necessary.
Keep the dialogs interesting, short and simple. Progress slowly from the general introduction dialogs to more varied aspects of conversation. Always have questions as part of the dialog. Chit chat is important. Most of us really don't talk about much that is meaningful so why give your students difficult subjects to talk about? How many of them really need to learn how to rent a car or book a hotel room? Yep, none of them do.
I've lost count of the horrible conversations I've seen in textbooks about faxing a memo to the director or complaining about the restaurant bill. It's bloody rubbish and just because textbook writers have heard the simple conversation scenarios a million times before, doesn't mean that students have or that they aren't useful for conversation practice.
Only native English speakers can teach English language conversation. That's you. And you can do a really good job of this is you are patient and you keep it simple and focused on the students.