Mathematical knowledge of pre-service teachers is currently "under the microscope" and the subject of research. This paper proposes a different approach to teacher content knowledge based on the "big ideas" of mathematics and the connections that exist within and between them. It is suggested that these "big ideas" should form the basis of teacher planning but it is acknowledged that this represents a "cultural change." The proposal is supported by results from a project that involved pre-service teachers in their final mathematics education unit. Results suggest that a focus on the "big ideas" of mathematics has the potential to change teacher planning and enhance content knowledge.