This study investigates the mediator role of teachers' work effort in the relationship between sustainable leadership and perceived school effectiveness. It employs the relational survey model. The data was obtained from a study group of 411 teachers. Three different measures were used in the study: "Sustainable Leadership Scale", "Perceived School Effectiveness Scale" and "Work Effort Scale". The findings showed that principals' sustainable leadership scores were above moderate level except for social sustainability. On the other hand, teachers perceived their school as effective and their work effort above moderate level. It was also found that there were significant positive high and moderate level correlations among variables. Sustainable leadership predicted both perceived school effectiveness and work effort. Finally, it was determined that work effort did not have a mediator role in the relationship between sustainable leadership and perceived school effectiveness.