This chapter introduces impact assessment in education as a strategic tool to understand the effects of interventions. It emphasizes that impact assessments go beyond academic achievement, examining if programs create sustainable changes at individual, community, and societal levels. The chapter clarifies the differences between outcomes, effects, and long-term impacts, providing tools to distinguish between academic, personal, and socioeconomic changes. It explores measurement, evaluation, and assessment, highlighting differences between performance, outcome, and impact evaluation, and discusses methodological and ethical challenges with context-specific approaches. The impact evaluation cycle includes model definition, evidence collection, data analysis, and reporting. It examines impact assessment, impact evaluation, and performance evaluation as parts of an evidence-based decision ecosystem. The chapter frames impact assessment as a strategic opportunity for transformation, learning, and accountability, providing vocabulary, distinctions, and tools for designing or interpreting educational impact assessments.