Social essentialism, the belief that members of certain social categories share unobservable properties, licenses expectations that those categories are natural and a good basis for inference.A challenge for cognitive developmental theory is to give an account of how children come to develop essentialist beliefs about socially important categories. Previous evidence from Israel suggests that kindergarteners selectively engage in essentialist reasoning about culturally salient (ethnicity) categories, and that this is attenuated among children in integrated schools. In five studies (N=718) we used forced-choice (Study 1) and unconstrained (Studies 2-4) categorybased inference tasks, and a questionnaire (Study 5) to study the development of essentialist reasoning about religion categories in Northern Ireland (Studies 1-3 & 5) and the US (Study 4).Results show that, as in Israel, Northern Irish children selectively engage in essentialist reasoning about culturally salient (religion) categories, and that such reasoning is attenuated among children in integrated schools. However, the development trajectory of essentialist thinking and the patterns of attenuation among children attending integrated schools in Northern Ireland differ from the Israeli case. Meta-analysis confirmed this claim and ruled out an alternative explanation of the results based on community diversity. Although the Northern Irish and Israeli case studies illustrate that children develop selective essentialist beliefs about socially important categories, and that these beliefs are impacted by educational context, the differences between them emphasize the importance of historical, cultural, and political context in understanding conceptual development, and suggest that there may be more than one developmental route to social essentialism. Development of essentialist thinking about religion categories in Northern Ireland (and the United States)Psychological essentialism is the belief that natural categories contain an underlying essence that conveys category membership and causes category members to share both observable and hidden properties (Gelman, 2003;Medin & Ortony, 1989). In some cases, essentialist thinking can be useful. For example, using "essentialized" categories for inference provides us with an important tool to reduce the complexity of incoming information to manageable levels, and allows us to organize what we know and make inferences about what we don't know. However, essentialist thinking can also be harmful and lead to overgeneralization or unwarranted assumptions of homogeneity, especially when essentialist thinking is applied to social categories (e.g. Diesendruck, 2013;Leslie, Cimpian, Meyer & Freeland, 2015). In this paper we examine the development of essentialist thinking about socially important religion categoriesCatholic and Protestant-in Northern Ireland, with particular attention toward how school and national context may contribute to differences in the use of social categories to guide inferences.Essentialist...