@Pascal ******
You apply for the DTV using an Embassy which is part of the Ministry of Foreign affairs.
You like to study at a school which is part of the Ministry of Education.
Yes, there are different types of soft power, but going to school can be done on any legal stay in Thailand.
As you might know, tourist during their holiday and in Thailand on a 60 day Visa Exempt Entry, love to visit Thai cooking schools for a day.
So get the correct visa for the purpose of your stay, I think for a 1 day cooking class, the DTV is a little over the top.