Class Notes is unlocked for use in multiplayer and training by completing Skullgirls' tutorial. Alternatively, purchasing the character color bundle DLC will instantly unlock all stages, including Class Notes.
As the stage where the tutorial lessons take place, this stage is minimalist and simply designed: the floor and background are made of large sheets of lined paper, consists mostly of white coloration and there is very little background movement (other than Mrs. Victoria's idle stance and poses). Standing next to a solitary blackboard is Mrs. Victoria, eager to teach her pupils the basics of fighting.
Humorously, Squigly fights Marie 300% in Class Notes during her faux non-canon story mode.