The aim of this research is to reveal the effect of teachers' participation in administrative decisions and their willingness to participate in decisions on school effectiveness. Predictive survey model was used in the study. In the 2021-2022 academic year, 283 teachers working in Istanbul's Sultanbeyli, Pendik, Maltepe and Kartal districts formed the research sample. Simple random sampling was used when selecting the research sample. According to the results of the research, teachers' willingness to participate in administrative decisions is significantly higher than their level of participation in decisions. In addition, there is a positive correlation between the level of participation in decisions, willingness to participate and school effectiveness. In addition, the level of participation in decisions and willingness to participate partially predicts school effectiveness. As teachers' level of participation and willingness to participate in decisions increases, school effectiveness increases.