The New York City Department of Education's (DOE) annual survey of parents, students, and teachers is the largest of its kind in the United States. The DOE relies on the survey to identify schools' strengths and to target areas for improvement. School Survey scores, along with attendance, are also the only non-academic indicators used in the DOE's annual Progress Reports for schools, which are used to evaluate school quality. Given these high stakes, it is important to make sure that the survey accurately captures parent, student, and teacher perspectives. Since 2010, the Research Alliance has been working with the DOE to assess and enhance the School Survey. Using data from 2008-2010, we examined the reliability and validity of the survey's measures, and made a number of recommendations about how the survey could be improved. This technical report, "New York City School Survey 2008-2010," presents a detailed account of our statistical exploration of the reliability and validity of the NYC School Survey. An associated brief, "Strengthening Assessments of School Climate," summarizes our findings and recommendations to date. It also outlines a set of broader lessons that have emerged from our work, which can provide guidance to the growing number of cities and states around the country that are implementing school survey efforts. Finally, the brief includes a note from Lauren Sypek, the DOE's School Survey Director, reflecting on the process of collaborating to improve the School Survey as well as some of the changes that have been made to the survey as a result of this partnership. Appendix A shows the number of schools by type for 2008-2010, along with the results for additional grade configurations. Appendix B briefly describes how school-level scores were calculated for reporting categories and provides additional details, including tables listing survey items by respondent. (Contains 29 tables, 12 figures, and 15 notes.)