A longstanding problem in the teacher workforce, internationally and in the UK, is the continuing and substantial numbers of qualified teachers who leave the profession within five years. This paper uses data collected from a survey to the last five years of teacher education graduates of UCL Institute of Education (IOE) in London, to explore what originally motivated them to teach, and the reasons why they have left or may consider leaving in the future. We discovered that despite claiming to be aware of the challenges of workload before entering teaching, workload was the most frequently cited reason for having left, or for leaving in the future. The data spoke to the reality of teaching being worse than expected, and the nature (rather than the quantity) of the workload, linked to notions of performativity and accountability, being a crucial factor. This paper draws on a substantial new source of data and explores reasons for leaving in the context of reported initial motivation of individuals who have left teaching, individuals who are planning to leave and individuals who are planning to stay in teaching.