Can you receive 90 days upon re-entering Thailand if you leave before an educational visa ends?

If you want 90 extra days from a visa by exiting and re-entering, it must be a multiple entry visa. Odds are that your education visa is single entry. You can still exit and re-enter (in principle - you may have problems actually doing it), but then you need a re-entry permit. That permits only qualifies you for the remainder of the original allowance. You don't get any extra time with it.

The only way to receive 90 days on entry to Thailand is to have a visa you purchased from a Thai embassy before you enter.

Or have a passport from Argentine, Brazil, Chile, Korea, Peru, or Russia.