You're right on, Yingweng. I agree completely. However, my students want me to speak in Thai when I introduce them to new concepts, so I try to do that.

And they're not the only ones. My fellow English teachers and even my boss want me to use Thai in those instances as well. So, I do what I'm told.

However, after I intro new material, I cut out my students' L1 completely. I go into 'English only' mode and TRY (often futily) to get my students to use as little Thai as possible. This has gotten me mixed results. Looking back after a year of teaching, I KNOW I could have taken my students farther if I would have used more Thai in the classroom. Especially the less-motivated students who were just starting to feel sex hormones raging through their blood.

Good luck,

HZ