This article explores the beliefs and practices of a high school biology teacher through three interrelated theoretical frameworks: common knowledge, collaborative learning, and communities of practice. The data were obtained from an in-depth case study of Maria, a biology teacher from a Mexican public high school that was participating in a 4-year international science project using collaborative learning and information and communication technology. Her beliefs and practices were explored by means of questionnaires, semi-structured interviews, and nonparticipant observation of classes. Through the use of the three-component framework, the degrees of coherence between practice and beliefs that guide the teacher's daily behavior became apparent, as well as the difficulties of incorporating innovations due to institutional constraints.