Primary processes in schools are hard to pin down despite attempts to measure central aspects of processes and outputs. For this very reason, it is important that teachers are motivated to go above and beyond their formal job responsibilities, a phenomenon called organizational citizenship behaviour. Social exchange theory is a theoretical explanation for organizational citizenship behaviour. This study examines a model of clear leadership and relational building between head and teachers as antecedents, and organizational citizenship behaviour as a consequence of teacher-school exchange. One purpose of this study is to explore the nature of exchanges between parties in the organization of teachers' work and examine the relative impact of these aspects on organizational citizenship behaviour. The methodology adopted was a cross-sectional survey of 234 secondary teachers. The structural equation analysis indicates a strong support for the importance of principal-teacher trust on social exchange and indirectly an impact on organizational citizenship behaviours. We also found some moderate support for the importance of clear leadership on organizational citizenship behaviours. This article presents suggestions for future research and possible implications for practice. (Contains 2 figures, 2 tables and 2 notes.)