This research analyses, using a case-study approach, the perceived success factors in an outstanding Chilean public school serving socioeconomically vulnerable students. This qualitative study draws on qualitative interviews with school staff and class observations, using the Instructional Core model as an analytical framework. Analysis revealed that the beliefs and structural cultural values shared by the school community where more relevant to explaining school success than concrete practices, and highlighted the importance of the interrelation among success factors for understanding their impact on school effectiveness. Additionally, elements such as the ongoing and changing nature of success factors, the strong influence of leadership and internal relationships and the use of professional judgement and situated knowledge by teachers were also identified as key to understanding effectiveness. Lastly, the unintended consequences apparent in this case-study are discussed, as the school under study confronts the hostile and inequitable Chilean education policy context.