Research on theory of mind increasingly encompasses apparently contradictory findings. In particular, in initial studies, older preschoolers consistently passed false-belief tasks-a so-called "definitive" test of mental-state understanding-whereas younger children systematically erred. More recent studies, however, have found evidence of false-belief understanding in 3-year-olds or have demonstrated conditions that improve children's performance. A meta-analysis was conducted (N = 178 separate studies) to address the empirical inconsistencies and theoretical controversies. When organized into a systematic set of factors that vary across studies, false-belief results cluster systematically with the exception of only a few outliers. A combined model that included age, country of origin, and four task factors (e.g., whether the task objects were transformed in order to deceive the protagonist or not) yielded a multiple R of .74 and an R2 of .55; thus, the model accounts for 55% of the variance in false-belief performance. Moreover, false-belief performance showed a consistent developmental pattern, even across various countries and various task manipulations: preschoolers went from below-chance performance to above-chance performance. The findings are inconsistent with early competence proposals that claim that developmental changes are due to tasks artifacts, and thus disappear in simpler, revised false-belief tasks; and are, instead, consistent with theoretical accounts that propose that understanding of belief, and, relatedly, understanding of mind, exhibit genuine conceptual change in the preschool years.