12 Month Stay in Thailand! How?
 

I want to go to Thailand and do a Maui Thai course, the course will run for 12 months. I was just a little confused on how one would stay for 12 months, since from what I can tell the visa is for around 60-90 days. I read that you can cross the border and the return through the same entry. Is this possible to just leave and enter the same day?

You can do "visa runs" but you need to research a bit as restrictions apply and it varies on your visa. They also change the restrictions from time to time.

Types of visa.
You can get a visa waiver if your country is in the visa waiver scheme (53 countries are) - this allows you 30 days without a visa (this may increase to 45 days - come October until March 2023.
Once in the country you can extend this at immigration for up to 30 days.
Doing visa runs - if you leave the country by land, you can re-enter (immediately if you so wish) but only twice in one year.
There is a limit of entries by air - I THINK it's 6 per year, but many people say they've never been checked.

A tourist visa is 60 days - this can be extended by 30 days - check this! (you need to prove you have 20000 baht on entry.
Then there is a multiple entry tourist visa (METV) - this lasts 6 months but requires more paperwork including a higher financial qualification.

Another one that MIGHT work for you is an EDUCATION visa - I don't know if this applies to a Muay Thai course, but it's worth asking the place you are training at.

Another way is to get a Non-Immigrant "O' type visa. Now again, you'll need to research how to qualify - there are several different kinds. They are normally valid for 90 days and extendable to a year. Most retiree expats have variations on this visa.

Some others to others to checkout are a sports visa or a "B" visa - business or work.

Suggest you ask your Qs at a Thai forum for more local info. AseanNow, formerly Thai Visa, only one i know. Google will hep you and click on Visa information etc.
I do know that for any 1 yr retirement Visa extension, you must be 50 yr old, and drop 800,000 thai baht into the bank. Or be married to a Thai lady for cheaper rate but more stress.