Brain teaser # 27

A duke was hunting in the forest with his men-at-arms and servants when he came across a tree. Upon it, archery targets were painted and smack in the middle of each was an arrow. "Who is this incredibly fine archer?" cried the duke. "I must find him!" 

After continuing through the forest for a few miles he came across a small boy carrying a bow and arrow. Eventually the boy admitted that it was he who shot the arrows plumb in the center of all the targets. "You didn't just walk up to the targets and hammer the arrows into the middle, did you?" asked the duke worriedly. "No my lord. I shot them from a hundred paces. I swear it by all that I hold.
Holy." "That is truly astonishing," said the duke. "I hereby admit you into my service."

The boy thanked him profusely. "But I must ask one favor in return," the duke continued. "You must tell me how you came to be such an outstanding shot."

How'd he get to be such a good shot?