The lost class of 1947 refers to a group of students from Bell Valley Middle School that disappeared in 1947. They were sent to the strange black and white dimension known as Grayworld. They appear in the Goosebumps book, The Haunted School.
Not much is known about them except a few minor details about one or two of the children's physical appearances. Sometime after being sent to Grayworld, the children eventually went crazy and fled the school due to being without color for so long. Soon after, they began a terrifying cult of sorts involving a pool of a oily black substance. According to the others who still remain in the schoolhouse, they cover themselves in the substance every night, having also created their own laws and strange beliefs unlike the other children who stay in the school. For their own safety they have apparently given up all hope of escape or rescue.
Once the two boys Tommy Frazer and Ben Jackson from the modern age of 1997 are transported into Grayworld they ignore Seth and the other kids' warnings about the other children and journeying outside the school and escape through a window once there they are ambushed by the other members of the missing class who are utterly surprised that the two still have color and this completely upsets them so that they surround them and begin a strange dance and chanting to turn them as gray as they are but when this fails once the boys try and get away the kids grab them and take them to the Black Pit where the black oily substance is to try and make them cover themselves in blackness like them but fortunately both are saved by Seth and the two girls Mary and Eloise at the last minute but still the other kids surround them as they attempt to once again escape until Tommy uses his lighter in which the bright blinding light and heat frightens and confuses the other children who scatter to safety but they soon try and return to capture them again only this time Seth and the two girls manage to lead both boys back to the safety of the school.