Discriminant validity of a measure of children's readiness for school was assessed by testing whether it distinguished between groups of children hypothesized to differ, on the basis of demographic characteristics, in their school readiness. The volunteer sample consisted of 3,370 kindergartners in Vermont public schools. Previous group care experience, identified learning-related disabilities, and a community-level measure of poverty were used as independent measures in analyses of children's readiness scores in four conceptual domains. Statistically significant relationships were found between prior group care experience and readiness in each of the domains, and between disability status and readiness in each of the domains. In addition, there were significant negative correlations between community-level poverty and community-level readiness in three of the domains. Results are discussed in terms of their value in establishing credibility for a school readiness measure that can serve to inform a community's efforts to address improvements in the early care and education of children. (Author)