By Jean Lee Latham
A poor boy in Salem leaves school at ten, gets bound out for nine years when he's twelve, and teaches himself enough mathematics to write the book that every ship in the world would sail by.
Nat Bowditch is small, quick, and desperate for school, and the family money runs out from under him. At twelve he's bound to a ship's chandler for nine years, which means nine years of copying other men's accounts before he's his own man again. So he teaches himself instead. First Latin, out of a borrowed dictionary, so he can read Newton. Then astronomy. Then navigation. When he finally gets to sea he starts checking the tables every ship uses to fix its position, and finds thousands of mistakes in them, the kind that had been putting ships on the rocks for a hundred years. So he writes his own. Sailors called it the Sailors' Bible, and it's still aboard ships today. And he does the thing the title comes from: he teaches the whole crew, the cook included, to work out their position by the moon, because he doesn't believe mathematics belongs only to gentlemen.
I'd hand this to a child who has decided mathematics is something done to them. Latham doesn't smuggle the math in around the edges and she doesn't water it down; she makes it the plot, so wanting to know how the trick works and wanting to know what happens next turn out to be the same wish. And Nat's life carries the rest. He loses the thing he wants at ten and gets it back years later by grinding at it alone, and your child gets to watch that happen page by page. It's 1955 prose and it moves, mostly in dialogue. Keep a globe within reach.