The Boy and the Fox
"So seriously did Spartan children go about their stealing, that a boy, having stolen a young fox and hid it under his cloak, let it tear out his guts with its teeth and claws and died right there, rather than let it be seen."
Learn by doing: write a different ending to this story
More about the Spartans
Plutarch's Lives Volume 1 (Modern Library Classics) by Plutarch , translated by Arthur Hugh Clough. Includes the biography of Lycugus that has the fox story in it.
The Spartans: The World of the Warrior-Heroes of Ancient Greece, from Utopia to Crisis and Collapse, by Paul Cartledge (2003). This is pretty hard going, but Cartledge knows everything about ancient Sparta.