@Graeme *****
was posted In here not long ago. Seems to be deleted now. Was daughter of OP that was denied entry, after leaving Thailand for 2 weeks, during Thai language course. They pulled here aside asking questions etc and probably ask about thai language skills. Where there was a ton of jokes about cooking classes needing to cook for IO.
I highly doubt everyone on DTV soft power visa, actually do the classes.
From what I read about these visa is they recommended that the courses have duration above 6 months. And if I going for DTV, it will be to attend to it. I'm never this long in Thailand. I'm normaly 2 times x 90 days in Thailand.