Depends on how many upgrades you have, and to what level you're going.
For starters, the education levels go every 10 points:
VERY LOW (10 and under)
PRETTY LOW (from 10 to 19)
DECENT (from 20 to 29)
PRETTY GOOD (from 30 to 39)
GOOD (from 40 to 49)
GREAT (from 50 to 59)
INCREDIBLE (from 60 to NICE)
THE BEST IN THE COUNTRY (70 and over)
Each class you gain one point (provided you don't use powers on the girls) and if you do Monday to Friday during Morning and Afternoon you will get 10 points, but each Friday you lose 5.
You need upgrades.
Buying the textbooks upgrade for the college adds one more point per class.
Same as checking one of the books in the library.
And getting teaching advice from Madison.
Also you can reduce the weekly points drop by 1 when you buy the decorative crystal from the merchant in the field.
Same as getting teaching advice from Veronica.
Meaning 4 points per class (40 for the entire week) with a drop of 3 at the end of the week.
So from 0 to the current required for max authority would be 11 to 12 classes.