De Wikipédia , proveniente da autobiografia póstuma de Heinlein Resmunga do túmulo :
Heinlein's original title for the novel was The Brass Cannon, replaced with the final title at the publisher's request.
O título provavelmente é inspirado na seguinte citação do romance (ênfase minha):
"I accept the title—nay, I glory in the title of 'jailbird.' We citizens of Luna are jailbirds and descendants of jailbirds. But Luna herself is a stern schoolmistress; those who have lived through her harsh lessons have no cause to feel ashamed. In Luna City a man may leave purse unguarded or home unlocked and feel no fear… I wonder if this is true in Denver?"
-- Professor de la Paz