@Sam *****
Then the answer is NO, you can't go from a 90 day Non-O entry stamp to an ED visa inside the country at the immigration office.
You can't change visa TYPES inside the country (except from a tourist to a Non-Imm).
OR
At least you can't do the switch "above the table" <- by showing up at the immigration office with paperwork from a school to apply for an in country Non-ED visa.