Sentence:  "I don't want to <WSD>spoil</WSD> any comparison you are going to make," said Jim, "but I was at Winchester and New College." ¶ "That will do," said Mackenzie. "I was dragged up at the workhouse school till I was twelve. [...]" 
Meaning of the word marked with <WSD> tags:  To ruin; to damage (something) in some way making it unfit for use. (from 16th c.)