Climate strength was first conceptualised in the organisational psychology literature as the within-group agreement on the perceptions of climate. In contrast to the deep study of climate level, climate strength has not been clarified by school climate research. The purpose of this cross-cultural study is to identify the main effect of disciplinary climate strength on student reading performance, and its moderating effect on the relationship between disciplinary climate level and student reading performance. A multilevel analysis was conducted on 2009 data from the Programme for International Student Assessment (PISA) from Shanghai-China, Japan, and the United States (US). The result showed a significantly positive relationship between climate strength and student reading performance in Shanghai-China and the US. Moreover, a moderating effect of climate strength was found in Shanghai-China and the US. The effects of climate strength were further examined in strong and weak conditions. School-level predictors of climate strength were also examined. The differences in disciplinary climate strengths and their effects on student reading performance suggested some culture differences in these countries/areas.