No

you could get a multi entry turist visa before going to Thailand. That would get you almost 9 months of stay in total, after which you could go to a nearby country and get another single entry visa for 60 days and extend another 30.. Or you could get either the single or multi entry before coming to Thailand, and then before that expires, apply for a one year extension at immigration based on being the guardian of your son. I believe that would require 500.000 baht in a thai bank in your name, I dont recall how long it has to be seasoned, but i am sure others here can tell you that.

The vast majority of immigration offices don't have an atm in the building anyways

Gregor Huettner atm card is not needed.. why do you say this? Just have the bank letter that states the account is yours, and what amount was in it at the time of the letter being written, together with the bank book and copies of the last few months from that book. ( months depending on what kind of extension)..

Not all accounts have an atm card, and I have personally never heard of anyone anywhere having to use an atm card to prove a bank statement for immigration.

if you are able to make the 30 extension more than once on your METV is up to the officer at immigration. There has been some people reporting they got refused more than a single extension pr visa

if your METV is still valid when you return you will get 60 days that can be extended by another 30 days at immigration. If not annika is right, you wil get 30 days and can extend that by another 30.. Its not possible to make more than one 30 day extension on each turist visa entry.

A re-entry permit (multiple or single) does not care about calendar years. It is valid from the date you get it, and keeps your current admitted to stay date alive. It does not give you any extra time than you already have on your existing visa or extension of stay. A single re-entry is invalidated as soon as you leave the country and re-enter again. A multiple re-entry is valid for the entire period your current visa or extension is valid for.

On a non O A you have one year of validity on the visa.. So within that year you will get stamped in for a year every time you leave and re-enter the country. You can exit and re-enter just before the date of expiry to get another full year of stay. But if you leave and re-enter the country after the original visa has expired, you will need to buy a re-entry permit as to not cancel the permitted to stay date you already have. If you are already on an extension of stay, from immigration inside Thailand, then you always need to buy a re-entry permit to not cancel your extension.

Okay then.. Nice to know :)

He stated that both schools ends in June 2019.. Are you saying that some schools would count that as being admitted until October?