Broke his duck's egg. Took his first school prize. In cricket a “duck's egg” or 0 in a score is broken by a run.
“What a proud and happy day it was to Lucy when little Herbert, in public-school parlance, `broke his duck's egg—otherwise, took his first prize.” —A Fellow of Trinity, chap.i.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894