Grades increase by 1 at discipline 61+ and by 2 at discipline 81+
Thank you for the answer. Previously I had reached chapter 2 but I chose to stop playing and wait for the latest update which will be out soon, discipline has not reached 60 so I don't know grades can still increase on condition that after chapter 2 or using cheats, I ask to make it easier to get popularity and grades because I always play while looking for the fastest way to finish the game (number of days in the game), even though it takes longer because of "save & load" to get the desired result. Previously grades could easily increase in chapter 1 but now it can only happen in chapter 2, my previous grade had never reached 100 because the previous version I played didn't need to reach 100, and the latest update that I played, I was lazy to collect grades up to a hundred to complete game, so I solved it with a cheat (only adding grades). But I hope in the next latest update I want to start over again without using cheats. Because using cheats it feels so less fun.