This study was conducted to determine the relationship between school climate, academic optimism and school effectiveness perceptions of high school teachers. Relational survey model, one of the quantitative research models, was used in the study. The research sample consists of 348 teachers working in different types of public high schools in the central district of Düzce province in the 2022-2023 academic year. "Demographic Information Form", "School Climate Scale" adapted into Turkish by Canlı, Demirtaş, and Özer, "Academic Optimism Scale" developed by Wayne K. Hoy (2006) and adapted into Turkish by Çoban and Demirtaş (2011), and "School Effectiveness Scale" developed by Hoy (2009) were used to collect the data. It was determined that the data were normally distributed, and Pearson Correlation Analysis, and Multiple Linear Regression Analysis were performed. According to the findings obtained, it has been determined that all the sub-dimensions of teachers' perceptions about school climate are at the “mostly” level. When looking at the concept of academic optimism, which is another variable, it was found that the “self-efficacy” dimension, which is the sub-dimensions of the scale, is at the “mostly agree” level in line with teachers' perceptions, while the “trust” and “academic emphasis” dimensions, which are the other sub-dimensions, are at the “moderate agree” level. It was determined that teachers' perceptions while their perceptions of school effectiveness were at the "moderate" level. As a result of the analyses, it was determined that there was a positive, statistically significant, and high-level relationship between teachers' school climate, academic optimism, and school effectiveness variables. According to the results of the analysis, it was determined that both variables significantly predicted the dependent variable, school effectiveness. However, it has been determined that school climate has a greater impact on school effectiveness than the academic optimism variable. For teachers to perceive school effectiveness at a high level, administrators' supporting teachers' efforts and encouraging teachers to ensure the continuity of these practices by giving feedback on good ones can help the school achieve its expected goals.