Tractate Bava Batra preserves a strange debate about classroom size that turns, without warning, into a story of life and death.
The rabbis were arguing about elementary education. Twenty-five children, they said, is the maximum for one teacher. At forty, you need an assistant. At fifty, two teachers. Then Rava and Rav Dimi of Nehardea began to disagree about whether it is better to teach much superficially or little thoroughly.
To defend the danger of superficial teaching, Rav Dimi told this story.
When King David sent Joab to war against Edom (1 Kings 11:15-16), Joab remained there six months and killed every male. David was furious. "Why only the males? Why not the whole remembrance of them?"
Joab replied, "Because it is written, 'You shall blot out the zachar — the male — of Amalek' (based on Deuteronomy 25:19)."
"But," said David, "the verse says zeikher — remembrance — not zachar."
Joab replied, "My teacher taught me to read zachar."
The teacher was sent for. He had taught the boy a single vowel wrong, and the mistake had become a nation of orphans. The court condemned him, and the teacher pleaded in vain for his life.
The story is chilling on purpose. The rabbis wanted every teacher of small children to feel the weight of a mis-taught vowel — because one careless lesson, repeated at scale, can rewrite a war.