When does the 90-day reporting period start for my education visa in Thailand?

Like Charles said, you so far have not had a visa that lets you stay in Thailand more than 90 days, so you haven't needed to do a 90 day report. When you get your first ED extension is when it starts as that will be the first chance you'll have had to officially be in the country on an extension over 90 days. They will give you the slip of paper then that will tell you when your next 90 day report is.

Possibly neither... Did you get the slip telling you when to report?

I came in visa visa exempt and then inked ED in at div 1. I did not start the 90 day reporting period until my first extension of the ED. This is when I got the white slip of paper from. Immigration telling me when first report was due.

This was confirm with Todd too, as it confused me.

From the day you entered the country