Evidence confirms that student skills other than academic achievement and ability predict a broad range of academic and life outcomes. This evidence, along with a new federal requirement that state accountability systems include an indicator of school quality or student success not based on test scores, has sparked interest in incorporating such "non-cognitive" or "social-emotional" skills into school accountability systems. Yet important questions have been raised about the suitability of extant measures of non-cognitive skills, most of which rely on asking students to assess their own abilities, for accountability purposes. Key concerns include the possibility of misleading information due to reference bias in students' self-reports and that students may simply inflate their self-ratings to improve their school's standing once stakes have been attached. The most ambitious effort to deploy common measures of non-cognitive skills as part of a performance management system is unfolding in California's CORE Districts, a consortium of nine school districts that collectively serve over one million students. In the 2014-15 school year, CORE conducted a field test of measures of four social-emotional skills involving more than 450,000 students in grades 3-12. Starting this year, information from these measures will be publicly reported and is expected to play a modest role in schools' performance ratings, comprising eight percent of overall scores. Analysis of data from the CORE field test indicates that the scales used to measure student skills demonstrate strong reliability and are positively correlated with key indicators of academic performance and behavior, both across and within schools. These findings provide a broadly encouraging view of the potential for self-reports of social-emotional skills as an input into its system for evaluating school performance. However, they do not address how self-report measures of social-emotional skills would perform in a high-stakes setting--or even with the modest weight that will be attached to them within CORE. The data currently being gathered by CORE provide a unique opportunity for researchers to study this question and others related to the role of schools in developing student skills and the design of educational accountability systems. The following table is appended: Social-emotional skills assessed by the CORE Districts. Contains endnotes.