The Expanded Success Initiative (ESI) evaluation was designed with two overlapping and interacting components: (1) a study of the initiative's implementation in the participating high schools; and (2) a study of its impact on student experiences and other outcomes. As the document of record evaluating an important, large-scale initiative, this report sets out to answer a number of key questions about ESI's implementation and impact. Specifically, the report examines ESI through the lens of the initiative's theory of action by assessing: (1) the district-level "inputs" of the initiative, including funding, professional development, and the creation of cross-school learning communities; (2) school "actions," including developing and expanding programs, supports, and services within ESI's three core domains; (3) participation among teachers and students in ESI related activities; (4) ESI's influence on school culture and relationships; and (5) its impact on students' perceptions of their schools, their high school experiences, and a number of student outcomes, including graduation and college enrollment. While this report is comprehensive, the hope is that individual sections and chapters will be of interest to different stakeholders, including policymakers, district leaders, educators, and community organizations. And in addition to providing a summative set of findings about ESI, the hope is that this report will provide a useful lens by which to examine and understand other initiatives focused on Black and Latino young men (and other underserved populations). [For the technical appendices, see "The Expanded Success Initiative: Challenges and Progress in the Pursuit of College and Career Readiness for Black and Latino Young Men. Technical Appendices," ED591648.]