An attempt is made to demonstrate that major theories of children's outdoor play reveal the social class biases of their originators. Most modern play theory is enclosed in the individualism of Western philosophy; its emphasis on the voluntary, the solitary, and the creative are seen as indications of its cultural relevance to people of higher economic status. Another kind of play theory, that play is a way of organizing and attenuating baser instincts through collective character training activities, is described as a way of improving the behavior of the poor, which is perceived by the rich as depraved and deprived. A schematic outline of a new sociology of play theory from a psychologist's perspective indicates that no description of play can ever be sufficient if it does not make explicit its cultural as well as its psychological assumptions. It is suggested that there is always a psychological function of mind at work in play, but always within a specific and relative framework. An implication of the examination and reformulation of play theory is that a fundamental re-examination of the informal-formal balance within the school system is called for. (Author/AMH)