This book leverages data from two major international large-scale assessments—the Trends in International Mathematics and Science Study (TIMSS) 2019 and the International Civic and Citizenship Education Study (ICCS) 2016—to investigate the extent to which education for sustainable development learning outcomes, such as environmental knowledge and willingness to act pro-environmentally, are achieved and fostered in various educational systems. This concluding chapter highlights the most important findings from the empirical chapters, organizing the discussion around the three specific research questions that guided investigations. These include a focus on: (1) analyzing variations in environmental knowledge and willingness to act pro-environmentally across different countries; (2) exploring potential disparities among students within countries, particularly how various background characteristics shape potential inequalities in learning outcomes; and (3) assessing the implementation of educational opportunities for learning about environmental sustainability in lower-secondary schools, and exploring how these opportunities are associated with students’ learning outcomes. Moreover, the chapter includes a reflection on ways to further enhance the relevance of international large-scale assessments such as TIMSS and ICCS for understanding key education for sustainable development learning outcomes and processes.