Religious pluralism led to the colonies' separation of church and state by 1776, to Mann's campaign for common schooling, and to the complete secularization of public schools by 1900. The dependence of Western theology upon untenable Greek metaphysics justifies an explanation that the evolutionary purpose of religion was to promote personal integration and social cohesion. This also occurs in civic religion, herein explicated as the common faith established by truths from intersubjectively valid inquiries and by experienced qualities (i.e., the goodness) of things in the natural, societal, and lived worlds of the natural and social sciences and humanities. This promotes natural piety and a sustainable planet by grounding education in the child's being in the world. The inclusion of formal religion in the public school curriculum is considered, but unnecessary, because schools already promote individual development and social cohesion through education for citizenship, etc.