Over the years, age differences in the quality of social and cognitive play behaviours of young children have been reported. For example, Rubin, Watson, and Jambor (197X) indicated that preschoolers engage in significantly more unoccupied, onlooker, and solitary play and in less group (i.e., associative or cooperative) play than kindergarten children. Kindergarten children have also been found to display significantly more dramatic and less functional play than preschoolers. When the cognitive play categories of Smilansky (1968) are nested within the social play categories of Parten (1932), preschoolers have been found to engage in significantly more solitary-functional and parallel-functional, and in less parallel-constructive, parallel-dramatic, and group-dramatic, activity than kindergarten children (Rubin et al., 1978). Both Parten and Smilansky believed that their respective conceptions of play represented sequential, developmental hierarchies and that, over the course of time, children are expected to exhibit increasingly mature modes of behaviour. For example, at one time period a child might be involved in a large amount of parallel play which, with experience and social-cognitive growth, might diminish only to be replaced by group activities. Earlier reports using the nested Parten-Smilansky play scale were based on crosssectional data, thereby negating the possibility of examining developmental changes in play behaviours over time. Moreover, there have been few studies that have employed either the Parten or the Smilansky categories in a longitudinal fashion. Recently Smith (1978), in a study of 2-, 3-, and 4-year-olds, found an increase in group play and a decrease in solitary play over a 9-month period, thereby providing some support for the sequential development of social play. Unfortunately, longitudinal data concerning the Smilansky categories are non-exislenl. Thus, the purpose of the present study was to examine changes in children's observed play behaviours over four time periods within a given school year. It was expected that changes in play over time would take place in progressive directions