My Mrs has taught it for 25 years to a few off here with great results, one learned to speak read and write to a high standard in 3 years. I could not do that in 100 years and gave up years ago, still very, very basic. Never came across a situation where Thais were pleased you were trying, usually the opposite where they seem determined not to even try and understand. Tones are the big problem, can't even hear them unless they are exaggerated.