School dropout is a complex educational and social phenomenon in which learners leave formal education before completing the level in which they are enrolled or before obtaining an expected qualification. It is rarely the result of a single event. Rather, it usually develops through a cumulative process of disengagement shaped by individual, family, school, community, and structural conditions. This review examines the concept of school dropout, its major theoretical explanations, its principal risk and protective factors, and its psychological, social, educational, and economic consequences. Particular attention is given to poverty, weak academic achievement, grade repetition, absenteeism, low school engagement, family responsibilities, distance to school, school climate, bullying, disability, gender-related pressures, and the perceived relevance of education. The paper also discusses early-warning systems and evidence-informed prevention strategies, including academic support, psychosocial services, family-school partnerships, inclusive education, financial and transportation assistance, flexible learning pathways, vocational guidance, and re-entry programs. Current international evidence indicates that dropout prevention is most effective when it is proactive, data-informed, student-centered, and coordinated across schools, families, social services, and public institutions. The paper concludes that reducing school dropout requires not only keeping students physically enrolled, but also ensuring that they experience meaningful learning, belonging, safety, support, and realistic pathways toward further education, training, employment, and social participation.