In this dissertation I consider traditional approaches to developmental questions, and suggest new methods for analyzing variability in individual children. In chapter I, I review the literature on children's reasoning about mental states, such as beliefs and desires, from a very early age. This ability is often called "theory of mind". In chapter II I explore the suggestion that change in a preschooler's theory of mind is motivated by change in their executive functions, which reflect the

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... 's ability to manipulate abstract representations. To this end, a new measure of cognitive development in executive functions is tested empirically. A correlation between theory of mind performance and executive function performance is demonstrated. In chapter III, I go beyond correlations in groups, to address the question of individual development. Current theories of how theory of mind develops do not make any specific predictions about what developmental change looks like in individuals. Is change abrupt or is it gradual? Is there a universal path to mature performance, or are there inter- and intra-individual differences? A new method for statistically analyzing variability in individual children's performance is proposed. Findings are discussed in terms of a general theoretical framework for theory of mind development in chapter IV.