While the conceptual link between teachers' knowledge of reading-related concepts and student reading outcomes is widely acknowledged in the field, few studies have empirically examined this correlation regarding student reading comprehension. Thus, the present study investigated the association between upper elementary teachers' (N = 103) knowledge of reading comprehension, classroom instruction, and students (N = 1871) reading comprehension scores. Using a series of Hierarchical Linear Models to control for the nested nature of the data, findings revealed a significant interaction between teacher knowledge and classroom instruction. Specifically, students provided with good to excellent instruction by teachers with high knowledge (i.e., 1 standard deviation [SD] above the mean) tended to score statistically significantly higher on measures of reading comprehension than students provided the same quality of instruction by teachers with low knowledge levels (1 SD below the mean), controlling for students' grade level and the percentage of schoolwide students participating in the free and reduced-price school lunch program. These observed statistically significant associations were small to moderate in magnitude. These findings help validate theoretical accounts alluding to the critical role teachers' knowledge plays in moderating student reading outcomes.