In the spring of 2015, many states began administering new state assessments designed to measure students' mastery of the Common Core State Standards (CCSS) in mathematics and English language arts (ELA). This was the first wide-scale assessment of student mastery of the Common Core. For some states, it was also the first time that state math and ELA tests were administered on computers. Several states gave Common Core tests developed by one of the two state testing consortia, Smarter Balanced and the Partnership for the Assessment of Readiness for College and Careers (PARCC), while other states administered their own state-specific exam. To learn more about districts' experiences in preparing for, administering, and using data from the spring 2015 Common Core-aligned assessments, the Center on Education Policy (CEP) administered a survey from January to April of 2016 to a nationally representative sample of 418 superintendents or their designees in states that were implementing the CCSS. The survey also included questions about testing in general and other aspects of Common Core implementation, such as stakeholder support for the standards. A total of 276 district leaders responded to our request. Responses were weighted to be representative of districts in CCSS states. More information about methodology and sampling procedures can be found in the online appendix to this report at www.cep-dc.org. This report describes the findings of the survey of district leaders and includes tables with the response data. In the discussion of the data in the tables, highlighted are those differences that are statistically significant or noteworthy for other reasons. Many respondents took advantage of opportunities in the survey to explain "other" responses to particular questions or respond to an open-ended final question inviting additional comments on their experiences with the Common Core standards and assessments. Selected quotations from their written comments are interspersed throughout the report. All percentages, standard errors, and confidence intervals for the data in this report, along with a complete list of responses to open-ended questions, can be found in the online appendix.