A little hint to hold "Grades" and "Discipline" high at the first 2 weeks:
1. punish the girls only in the evening not in class (each + 1 discipline and grades points before fullfill quests)
2. train Miss Potts first of all (do Mr. Wilson´s visits/quests later or mostly on Wednesday evenings)
so you loose less discipline points when Miss Potts can controll her class better.
3. prefer cleaning punishment before spankings if you can ever affort (spankings earn most the money) and have changed the rules for public punishments. (+2)
4. join the girls at Monday evenings help with maths (+ 1 grades)
5. don´t use "uniform inspection" when you find the girls as group on patrol (+ grades)
6. be strict with clothes Amy, Debbie and Cassandra wearing on the first 3 weekend patrols to provide - discipline (you can be milder later and earn publicity points later in game)