@Tobias **********
Which begs the question WHAT did the school you're thinking of enrolling in tell you? 😮
As a rule you enroll, pay the tuition, the school applies for paperwork from the Ministry of Education, that takes any where from 2 to 6 weeks, THEN you can take that to the immigration office inside the country and apply for the 90 day ED Visa for 2000baht. That application goes under review for 2 weeks and then you go back to get the Non-ED visa and a new 90 day stamp inked in
SO if you actually have to leave on the 8th of Oct (which is 18 days from now) I'd say nope you can't get an ED visa inside the country.
BUT
again, TALK TO THE SCHOOL YOU'RE ENROLLING IN.. 🙂 they will know