The paper underscores the complexity of school dropout as a research topic, emphasising the challenges of comparison of data from various sources, crucial for policy and practical interventions. Despite extensive research, there is no universally accepted definition of school dropout, and national and international documents often conflate early school leaving (ESL, ELET) with dropout, leading to inconsistencies in data collec-tion and reporting. This overlap obscures certain groups, such as repeat-ers and students in “educational mortality”, who, while not formally clas-sified as dropouts, should be included in the discussion. These defini-tional ambiguities result in incompatible data collection methods and hin-der coordination among educational agencies, complicating the develop-ment of cohesive intervention strategies. The paper reviews key defini-tions from various documents, illustrating how this umbrella effect com-plicates understanding the issue. Additionally, it discusses findings from the doctoral project “School Dropout and Dropout Data”, which system-atically analysed 2,078 scientific articles on the subject. The study high-lights the need for shared data systems to accurately monitor the phe-nomenon and develop effective strategies. A reliable understanding of school dropout is crucial to avoid misinterpretation and to guide targeted interventions, particularly at the local level.