Thai speakers do it better
It's a stone cold fact that the most-liked foreign teachers at my school are those that can either speak Thai fluently or at least to a basic conversation level. They get the most respect from students and have no problems with basic commands, explaining worksheets and tasks and maintaining order in the classroom. I've read a number of articles on the internet about not having to be able to speak Thai in the classroom in order to be successful, but I'm not so sure, particularly when faced with a classroom of 40 rowdy and easily distracted teenagers.
Steve