This article reports on an in-depth case study of a novice middle school EFL teacher's cognition development during the process of learning to teach in the workplace. Data was collected mainly through classroom observations and interviews. Results indicate that the teacher exhibited a considerable amount of change in her classroom practices, which could be attributed to a number of interconnected factors, including teacher experience, reflection on practice and the teaching context. In relation to the behavioral adjustments, the teacher's cognition has also changed in varying degrees. It is concluded that the development of teacher cognition is the result of the cyclical interaction between the teacher's knowledge and belief system and her classroom practices. This study helps understand the nature and the process of teacher cognition development in the real workplace.