I have not seen anyone posting they were asked to show this at a port of entry. If they were they would need to show the classes were booked, maybe by a letter from the school and a paid invoice.
Back in the days of Lonely Planet Forums etc they were a running joke. I have never ever worn a pair I am glad to say. I did have a Samui t-shirt that last 15 years though
You need to check with the Embassy regarding sponsor. Most sponsorships tend to be for dependents only. There was a post in this group about a parent sponsoring a child. I do not think all embassies accept this though