The informant had heard the tale from his cousin whose primary residence was in Delaware. The informant was around 12 years old when he heard it.
Long ago, there was a woman notorious for her promiscuous affairs with many men. After having birthed her 11th child each from a different father, she met an old man who warned that if she continued her behavior, her 13th child would be a demon. Sure enough, the woman birthed the 13th child, who was born with the head of a goat and the wings of a bat. The demon then killed its mother and the mid-wife. Subsequently, while the Jersey Devil has never been spotted, mysterious claw marks have appeared in new homes and construction sites, among which was the middle school that the informant’s cousin attended.
It seems that this urban legend gives rise to the taboo nature of a woman’s sexual promiscuity. Being that Delaware’s predominant religious denomination is Catholic, the story’s chastisement of adultery appears consistent. Also worth noting is that the the cursed child was the 13th. In many cultures, including our own, the number 13 often connotes misfortune and dark magic superstition (i.e. “Friday, the 13th”). But beyond the sexual undertones of the story, I would guess that the appeal of the story to middle schoolers lies in the possibility of a mythical creature that has survived the test of time. As for the aesthetic of the story, that this creature has not been sighted while “evidence” (the claw marks) of its existence is prevalent scratches away at a community’s fear of what cannot be controlled. Further inquiring into how the informant’s cousin first learned the story would be useful in determining whether the tale serves as a tool by parents to keep children safe or if it merely functions as a means of entertainment, as it did in the transmission from the cousin to informant.
For another reference to the Jersey Devil, see also: http://www.csicop.org/si/show/the_jersey_devil_the_real_story/