The authors review several case studies of children engaged in rule-governed play and conclude that the process of learning rules--and of breaking them and making new ones--promotes what they call gamesmanship. They link the development of gamesmanship to the theory of Machiavellian intelligence, which considers social interaction primary in the evolution of human intelligence. They also question the benefits of adult-managed child play and assess the impact it may have on the ability of children to develop gamesmanship. (Contains 54 notes.)