This four-year longitudinal study examines the transitions of an early-career teacher from her completion of a graduate program with English certification (grades 7-12) into teaching literature in an urban high school. Our central question was how Beth's pedagogical knowledge was shaped over time by her consistent efforts to enact two key principles: (1) the centrality of students' meaning making and (2) the need to maintain high academic expectation for all students. The tensions that resulted from her department's stances toward these principles led to consequential transitions (Beach, 1999, 2003) for Beth's learning and development. An activity-theoretical analysis showed that over time Beth's development was shaped by the values, experiences, and practices of other teachers in her immediate professional communities and in contexts external to the department. Rather than relying on a single activity setting, Beth's pedagogical knowledge and practices developed out of an interweaving of conceptual and practical tools based on the constructivist principles of her teacher education program, her deepening knowledge of English studies, her students' learning, her enactment of new teaching practices, and her involvement in this longitudinal research project. This study raises questions regarding stage theories of teacher learning and development, suggests a horizontal notion of teacher development grounded in sociocultural theory, and provides evidence for the positive and lasting effects of teacher education and reflective practice. (Contains 3 tables and 2 notes.)