School self-evaluation based on multiple data sources has been used to evaluate the quality of education at schools. This study aims to reveal the state of the education process, health, safety, relations and communication, and participation in management at school. The study is conducted with a case study design, in a public secondary school. The researchers developed a School Self-Evaluation Model Supporting School Development and applied it to this study. In this study, two study groups were formed through purposeful sampling. Data was obtained from students, parents, teachers, and school administrators during the quantitative phase of the study, and these stakeholders were interviewed during the qualitative phase. In addition, while directing the implementation of their planned approach at the school, the authors conducted observations. The materials used to support the quantitative and qualitative data were also evaluated, and possible indicators were identified. According to the research findings, the stakeholders had good perceptions of the education processes in the school. Furthermore, the views of the stakeholders based on health, safety, relationships, and communication, participation in school management are also generally positive. However, it has been determined that there are some problems in student nutrition services, student relations, and participation in school management. All told, the stakeholders have generally satisfied with the education process at school. These findings have pointed out that school self-evaluation is very applicable for the constant improvement of schools based on various evidence.