Formal and informal leadership characteristics of the school administrator have a great importance in the development and effectiveness of the school. In this direction, it is aimed to examine the relationship between leadership and school effectiveness levels with the meta-analysis method. For this purpose, it has been investigated whether there is a significant difference between the effect sizes of the studies examining the relationships between leadership and school effectiveness levels according to the moderator variables. The studies examining the relationship between leadership and school effectiveness levels in the years 2010-2020 including the number of samples and correlation coefficient were included in the study. The studies within the scope of this study were accessed by scanning in national and international databases (Council of Higher Education Thesis Center, Web of Science, Education Resources Information Center (ERIC), Scopus, EBSCOhost, etc.). As a result of the literature review, 22 studies that were following the selection criteria of the research were included in the meta-analysis. In the study, "Fisher's Z" value was used to calculate the effect size values. Overall effect size of the studies within the scope of the study were calculated according to the random-effects model. As a consequence of the analysis, it was found that the overall effect size of the relationship between leadership and school effectiveness levels was positive directional and stronge. Moreover, it was observed that there was significant difference between the effect sizes of the studies examining the relationships between leadership and school effectiveness levels according to the moderator variables (location of the study, type of school and leadership types). Supporting the development of school administrators on teaching processes and objectives will increase the effectiveness of schools.