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, especially regarding student reading comprehension. Thus, the present dissertation study aimed to investigate teachers' knowledge of reading comprehension in a group of elementary teachers (n = 240) who had received professional development focused on evidence-based reading comprehension instruction one year prior to taking part in the study. Moreover, as these teachers had implemented evidence-based reading comprehension instruction for one year, the present dissertation also examined the link between the upper elementary (i.e., Grade 3-5, n = 103) teachers' knowledge and skills of reading comprehension, classroom reading comprehension instruction, and student (n = 3,514) reading comprehension achievement at the end of the school year. First, the Teacher Knowledge of Reading Comprehension (TKRC) survey was developed and examined for reliability and validity. Results found the TKRC to be a reliable (Cronbach's [alpha] = 0.85) and valid measure (i.e., explaining 57% of the variance) of teachers' content and pedagogical content knowledge for comprehension. Next, the relationship between teachers' knowledge on the TKRC, classroom instruction, and students' reading comprehension scores was analyzed. Using a series of Hierarchical Linear Models to control for the nested nature of the data, findings revealed that there was a significant interaction between teacher knowledge and classroom instruction. Specifically, based on an observation of classroom instruction, students provided good to excellent instruction by teachers with high knowledge tended to score statistically significantly higher on a standardized measure of reading comprehension (i.e., the Gray Silent Reading Test) than students provided the same quality of instruction by teachers with low knowledge levels, controlling for grade level, school SES level and teacher characteristics (i.e., years of experience, advanced degree, certification type, self-perception, self-reported amount of prior reading-related professional development). These findings help validate theoretical accounts alluding to the critical role teachers' knowledge plays in moderating student reading outcomes. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]