My favorite part by far:

The boy saluted formally. "Teach me no more, bondsman. Today i teach you."

A few pages later...

"Have you come here for a serious purpose, boy?"
"I have come for a serious purpose."
"Have you come as an outcast from your father's house?"
"I have come so." And would remain outcast until he had bested Cort. If Cort bested him, he would remain outcast forever.
"Have you come with your chosen weapon?"
"I have."
"What is your weapon?" This was the teacher's advantage, his chance to adjust his plan of battle to the sling or spear or bah or bow.
"My weapon is David."
Cort halted only briefly. He was surprised, and very likely confused. That was good.