The objective of this study is to contribute to the increasing database regarding the effects of school leadership on teachers' data usage by investigating the relationship between the technological leadership behaviors of school principals and data-driven decision-making at their schools based on the mediating and moderating effects of the knowledge management variable. 408 teachers from 14 provinces of Turkey in the 2020-2021 academic year were included in the study. The School Principal Technological Leadership Competency Scale, the Knowledge Management Scale, and the Data-Driven Decision-Making in Schools Scale were used as data collection tools in this cross-sectional quantitative study. Descriptive statistics, correlation, and structural equation modeling (SEM) were used in data analysis. The study results demonstrate the school principals' practices of technological leadership, knowledge management at schools, and data-driven decision-making to be high. It has been found out in the study that knowledge management implementations play a mediating role in data-driven decision-making at schools by increasing the technological leadership competency levels of school principals, while not having a moderating effect on the relationship between technological leadership and data-driven decision-making. In addition, technological leadership and knowledge management have been identified to be significant and positive predictors of data-driven decision-making. Based on the study results, suggestions have been made to improve the technological leadership behaviors and knowledge management implementations of school principals at schools.