School self-evaluation (SSE) or data-based decision making is now a common feature of mainstream education in an increasing number of jurisdictions. The participation of stakeholders including students, is promoted internationally as a key feature of effective SSE. Despite this, very little research has been carried out on how education systems might involve students in SSE and even less research has explored how student involvement can move beyond mere tokenism. Similar to many other jurisdictions, Irish schools are encouraged to include students in SSE. However, the research to date would indicate that while students are frequently consulted through the use of surveys they have little or no involvement in decisions that are made as part of the SSE process at a whole school level. This case study explores an atypical approach to student engagement in SSE which was tested in one Irish post-primary school where students participated as co-researchers along with their teachers in the SSE process. In doing so, student participation in SSE shifted from student as data sources to students as co-researchers. Students became members of the SSE Team, responsible for consulting with the wider staff team, student body and parents. They were actively involved in the completion of a whole school self-evaluation report on assessment and the development of a school improvement plan. The study outlines the key stages of the project and how student participation evolved through the process. Interviews conducted with both the teacher and student members of the SSE Team illuminates the experience of the students and staff on the SSE team. The findings indicate that this approach resulted in significant positive outcomes for the school and the individuals involved, but there were also a number of challenges. Student involvement resulted in greater awareness among, and participation of the wider staff team in the SSE process. However, it required more resources and time than is usually the case for an SSE process in Irish schools. The research suggests that this level of participation by students may require a more systematic and sustained engagement of students in decision making at a classroom level in order to build capacity of students to contribute to decision making at a whole school level on an ongoing basis. This study may have an application in jurisdictions aiming to include students in SSE, particularly at a higher level, and it also provides a glimpse into the deliberate planning and structures required if schools are to move beyond an instrumentalist, compliance model of ‘student voice’ towards a more authentic model of inclusive democracy.