This review of 25 school quality rating systems, written by Public Impact for the National Alliance for Public Charter Schools, reveals clear trends that may help rating system designers and users think about optimal system designs. The rating systems inventoried include some from state departments of education, large public school districts, charter associations and authorizers, and private news and advocacy organizations. Among the trends found were: the inclusion of student growth; the expansion of college- and career-readiness measures; an exploration of new ways to focus attention on the lowest-performing students; an interest in valid measures of student engagement; simplified reporting formats to categorize school quality; and an increase in data transparency and public accessibility. The review foresees a stronger system for evaluating quality across states following the adoption of Common Core-aligned assessments.