Steve Steven is that for any ED course, or just for formal University study (or full time school if under 18 etc.)? As I mentioned above in another reply, I studied at CMU on 1 year course, and was told that I would have to leave Thailand for new visa.
I had a course at Chiang Mai University, but not a formal (e.g. diploma or degree course) and was told that I had to leave Thailand for ED visa, even though I had a SETV. Possibly they don't know, or possibly, it is only available for a formal University course.
I have never heard of anyone doing a conversion of a tourist to a non-immigration visa for ED before. Only for retirement. Possibly a few others, but pretty sure not for ED purposes. Every school I have dealt with has told their students that they must get a new non-immigrant ED visa outside of Thailand, for which, they obviously must have their paperwork (although they don't need to be in Thailand to get their paperwork - it can, and regularly is, posted out)
TM30 also would mean that someone should be logged into the database at a particular address. For most extensions these days, they seem to be checking that the TM30 has been filed
Incidentally Tod Daniels, as a legal technicality, you can't 'buy' a visa, as 'buying' something infers ownership. You can pay for a visa as there is a fee involved, but not buy one (well, you can buy one if you pay for it illegally) :-)