Research on teacher and school academic optimism has abounded ever since these two constructs were confirmed and shown to have positive effects on student achievement. However, one overlooked research question is the nested association between teacher and school academic optimism. This study intends to fill this gap by using hierarchical linear modeling to empirically test the relationship between individual teacher academic optimism and collective school academic optimism. By using the data from 1073 teachers in 102 schools in Taiwan, the results show that around 10% of variance in teacher academic optimism came from school level, and that school academic optimism explained nearly all of the between-school variance as it overpowered a number of school contextual variables, such as percentage of minority students and student achievement, in predicting variation in teacher academic optimism. The implications of these findings for future research are discussed.