Selective mutism (SM) is typically identified in early childhood and is characterised by a lack of speech in specific social situations, usually at school. This study interviewed 11 teachers and used qualitative methods to develop an explanatory framework to represent the lived experience of teaching pupils with SM. Interviews were analysed using grounded theory methods. The final theoretical framework captured nine categories. This included five key processes: "categorisation" of teacher beliefs; the development and change in beliefs through a process of "scientific enquiry"; teacher efforts to "support" pupils; measuring and "monitoring" pupil progress; management of teacher "emotional responses," and four contextual factors; "pupil characteristics," "peer relationships," "teacher self-identity" and "staff relationships." The findings highlighted a link between teacher categorisation of SM and pupil support. Implications of the framework for guiding research and educator practice to support pupils with SM are discussed.