Juvenile delinquents serving time in jail, are given a test, then selected based on their results for a soldier training program being conducted by off worlders in conjunction with the military. As the story progresses it becomes clear that the children selected have a natural talent for war and strategy. Their maladjustment and inability to fit into society which put them in jail was due to their natural predilections not being put to proper use.
As they go through the training and find their natural place in society, the childrens attitudes transform for the better as they become men of war that view battle as the only game worth playing. Even the punishment of digging a pool for minor or major infractions turns from drudgery to joy as they evolve.
The story has a philosophical message about play and work. The closer to play on the matrix you are.. the better you perform and the more sane you are.