Simple walkthrough. (Not complete at all but this will help.)

The numbers of days do not mater.
MC must teach classes, to gain grade or to maintain them, if hit 0 game over.
MC must spank in office to make money for items and upgrades. (1 point of discipline each time.)
MC needs to spank sometimes in the classroom, this is not a must but it can help at times with discipline. (If discipline hits 0 game over, you get 2 discipline points doing this).(I will give 1 hint why this maybe a good idea, masochist. There is no difference but it may come in later updates.)
MC needs to do staff quest for Potts first and foremost to stop grades going down all the time and work on discipline as much as possible. (Low discipline = grades go down.)

Its very easy to do quest and all you got to do is read them for what needs to be done.
For those who skip unread text you are screwed because hints are in there.