In Act 1, the story eventually proceeds to the classroom where Sayori shows the protagonist to the other three memebrs of the Literature Club. The rest of the story runs normally until the player rushes out of the classroom to find Sayori dead.
Act 2 doesn't have much of any differences between its current state and in Act 1, however, some things do change in the room and persist until the end of Act 3. The story itself continues to use this area normally as a meeting place for the members, with the occasional darkening of the screen or "scripted glitch" taking place at certain times in the story.
In Act 3, the scene has completely changed and only one desk is visible to the player, with a few windows showing a strange and empty space-like background. The lighting is much different than before and appears to look like it is evening, despite Monika mentioning that time doesn't exist anymore in this version of the game.