Do I need to leave Thailand to validate my student visa, or can I start it upon arrival?

Sorry about that

@Inès ************

:O IF you hold a french passport you can indeed get stamped into the country for 30 days on the visa exempt program BUT you might have problems checking in for your flight here IF you do not have proof of onward travel OR a valid visa in your passport. So I would still say get a single entry tourist visa from a thai consulate BEFORE you come here. That will stamp you in for 60 days and will be plenty enough time for you to get the paperwork from your school.

As a rule UNLESS you're enrolling in a real university for a degree program you cannot get an ED visa inside the country and instead get paperwork from your school to go to a thai consulate in another country and get a 90 day single entry ED visa

There is no student visa :/ There is an ED visa <- the ED means education.

When you apply for the ED visa from a thai consulate it is valid for 90 days from the date it's issued <- That means you have 90days to ENTER thailand and when you do you'll be stamped in for 90 days.

As long as you get an ED visa from the thai consulate in your country BEFORE you come here, you'll be stamped in on that when you arrive.