Just to add to this, having a visa is no guarantee that the immigration officer will let you enter the country.

@Mikkel ******

I specifically meant him in his situation, yes, I know about the marriage and child exceptions

The only visa that will allow you to do work in Thailand is a Non-B visa, this requires a plethora of paperwork from the Thai company, and even if you have this visa, you are not allowed to do any work until your work permit has been approved, more paperwork, and this can only be applied for when you are in Thailand

@Karel ********

but also needs to do fulltime classes, so absolutely no freedom

@Charlene *************

you are good to go, dont worry and enjoy their visit

You cannot apply for an ED visa just out of your own, your first step is to find a school, they will provide you with the appropriate paperwork, only then can you apply

It will only be extended until your work permit expires, but you can apply for the extension anytime you have less than 30 days on your 3month visa left

I have just been through the same, although immigration CAN ask for the 3 proofs,

1. Proof of leaving Thailand within 30 days

2. Proof of accommodation for the entire stay

3. THB per person IN CASH

For a first time visitor they won't, this is more of a deterrent they have in their arsenal to have grounds for people abusing the visa-free system

You don't need to send anything, they will be granted 30 days visa-free entry upon arrival with no questions asked