Wisconsin's child care quality rating and improvement system, YoungStar, was created to improve the overall quality of child care through two strategies: increasing parents' knowledge about the quality of early care and education providers and supporting providers' efforts to deliver high quality care. The YoungStar rating system assigns participating child care providers a star level from 1 to 5 based on objective indicators of quality in four domains: education and professional training, curriculum and learning environment, business and professional practices, and child health and well-being. YoungStar is administered by Wisconsin's Department of Children and Families, who, at the time of the study, had contracted the operation of the program's regional offices, technical assistance, and rating implementation to a consortium of three organizations (Celebrate Children's Foundation, Supporting Families Together Association, and Wisconsin Early Childhood Association). In Wisconsin, the process of criterion indicator development and implementation was informed by other states' efforts and input from both experts and practitioners. An important goal for the Department of Children and Families has been to use empirical evidence to investigate whether the rating scale and the rating process work as intended to differentiate programs with respect to classroom quality and participating children's school readiness gains. The Wisconsin Early Child Care Study (WECCS) was undertaken to provide such an examination of the validity of YoungStar's rating scale. The study was designed to examine whether the rating scale is able to differentiate programs according to their levels of independently observed quality, and whether children who attend more highly rated programs gain more in terms of school readiness over the course of a school year than children attending programs rated at lower levels. This Executive Summary describes the finding s from two research reports that investigate these questions. (author abstract)