Pedagogical content knowledge is widely considered an essential and complex facet of mathematics teacher knowledge, but little research has focused on PCK at the senior secondary level. This study explores some of the complexities of PCK in a teacher's lesson for senior secondary students by analysing data from lesson observation, the teacher's own commentary on the lesson, and students' perceptions of the teacher's knowledge and actions. Findings suggest that classroom norms relating to the kinds of problems students are typically required to solve can affect priorities about what is taught, so that what is attended to and valued by students may impact on teachers' PCK demands.