I was at imigration with a friend the other day as she wanted to extend her VISA by 10 days... whilst there we were chatting with a woman who said she was having her ED VISA renewed there (as you have to every 90 days). I was lead to believe you had to leave the country every three months, am I correct and if so how come she could do it there?

Very confused =/

Koh Samui is a full fledged Immigration office and as such capable of renewing and extending visas. If your question is about the ED visa specifically and not Koh Samui Immigration then may I suggest moving this to the visas forum?

So I could renew my ED VISA here without going outside of the country... i.e. Malaysia / Laos etc?

I'll move this to the Thai Visas section as you will get the answers you need about ED visas there

Visa can not be renewed at any immigration office. If you have a multi entry visa you must exit Thailand and return yourself. Any travel of passport to obtain border stamps without you is illegal.

I have not seen any report of a 10 day extension being approved in the last year - was yours? It is normally 7 days maximum unless you have the tourist visa one time 30 day available.

There is an extension of stay available for language education which allows a new extension of stay every 90 days, upon presentation of TM.7/1,900 baht and proof of study. I suspect that is what you observed.

whilst there we were chatting with a woman who said she was having her ED VISA renewed there (as you have to every 90 days).

This sounds like confusion with the 90 day reporting requirement for a person who

has a one year extension on an Ed Visa.

Any person with a One year extension must report their current address to immigration every 90 days.

As Lopburi states, if you have a multi-entry visa, you MUST leave and re-enter every 90 days.