AFAIK: there is no private thai language school in Bangkok which makes you "show" you got an ED visa BEFORE you start studying. Sorry, ALL my experience is with schools in Bangkok.. (I don't get out much!).
In fact with the Ministry of Education back-logged by about 4-6 weeks, just to get the "invitation letter" from them so the school can issue you the paperwork to go outside the country and secure a single entry Non-Immigrant Type-ED visa (good for 90 days), you're studying thai almost a month BEFORE you get the paperwork to go get your visa.
While a LOT of schools "tout" the one year visa, what it really is (especially if they are private Thai language schools in Bangkok) is;AND
- A pile 'o paperwork to go outta the country and secure a single entry 90 day Non-ED visa
In Bangkok there is NO testing of students studying thai on an ED visa. Unless if by testing you mean the same old, "hello, how are you?" thai b/s pleasant speak which takes place.
- A subsequent pile 'o paperwork every 90 days after that to get an extension of stay for another 90 days.
IF you have your ducks in a row paperwork-wise Thai Immigrations just processes it and stamps you with another 90 day extension of stay.
I'd be interested to know the school you attend there Fluke, because by your profile you say you're in Chiang Mai. There's only a finite number of places you could be studying thai which are registered by the MOE. Some are good, some not so..
Good luck with that 90 day test of the thai language dealy...