Hi, am about to apply for the first leg of my ed visa 90 day portion (or whatever its technical name is ) outside Thailand and I wonder if I just pay for single entry now can I convert it to multiple entry later at the 90-day point at immiigration in case a family member is sick etc and I have to go out and back in to Thailand within the study year ?

No, you can't.

But in case you need to travel outside of Thailand you can get a re-entry permit that allows you to leave and come back without the need of a new visa. It keeps your permission to stay alive.

Thanks, that is probably all I'd need....sudden re-entry permit permission to go back home.

Thanks, that is probably all I'd need....sudden re-entry permit permission to go back home.

The re-entry permit will only be valid for the period of your current permission/extension of stay. It doesn't mean you can come back any time you'd like. If you're out of Thailand when both your permission to stay and re-entry permit expire, you will not be readmitted on the same basis as before without obtaining a new visa.