This article explores a case study of a mindfulness teacher, Beth, and her experiences of teaching mindfulness to 11- to 16-year-olds in several English schools. It shows why Beth was drawn to teaching mindfulness, which was both to alleviate the stress amongst her pupils and improve her own mental health. It illustrates how and why she became a confident, successful mindfulness teacher: she learnt about mindfulness at various classes, retreats and teacher-education training sessions, spending thousands of pounds on her own training. It argues that her positioning as a mindfulness teacher in an unmindful school system created an overwhelming demand for her services, but also huge stress upon her. It develops McCaw's conceptions of 'thin' and 'thick' mindfulness (2020), arguing that while Beth began by practising 'thin' mindfulness -- seeing it as a way of solving exam stress amongst her pupils -- she became increasingly a 'thick' practitioner; her experiences of mindfulness led to profound personal change and, ultimately, to her becoming very disillusioned about teaching mindfulness in an unwelcoming educational, 'unmindful' environment.