The only teachers I have found to help me add to my Thai skills all carry foreign passports. I found the Thai courses given by Thais very regimented and focused on topics, week by week , such as police one week , hospitals the next I found basic communication skills , followed by 3 years of learning Nouns and the Verbs was helpful.
Schools didn't focus or were willing to help with the areas of the language I wanted to learn.
PS books were useless ( before the internet days )
Now we have apps that are somewhat useful , but often incorrect.