Research Findings: This study examines the complexities of enacting an explicit content-rich curriculum in a large urban school district. Thirty-six teachers from 12 elementary schools, preK through Grade 1 were recruited to teach the "World of Words," an integrated science and literacy supplementary curriculum. Prior to the start of the study, teachers completed two self-reported surveys on their knowledge of science and pedagogical practices; their classroom lessons were subsequently audiotaped after several weeks of instruction. Results indicated that despite explicit guidance in the curriculum to engage in higher-order questioning, teachers' questions and comments remain strikingly low-level (63%). Subsequent case studies of four teachers, contrasting high or low levels of content knowledge and pedagogy showed that the higher content "and" pedagogy teacher engaged more successfully in enacting the curriculum with integrity. These results suggest the need for greater attention to teachers' content knowledge and applications to practice in professional development. Practice or Policy: Findings provide suggestive evidence for a greater emphasis on the integration of domain-specific content and pedagogy in teacher professional development, if we are to support high-quality implementation of content-rich curriculum.