While it is recognised that prior knowledge is a key factor in determining future learning, its influence on learning to teach is less well known. This study investigates two cohorts of teacher candidates studying for a one-year, graduate qualification for primary teaching, who completed two tasks at entry to their initial teacher education programme: a task in writing and a task in mathematics. The tasks focused on teacher candidates' ability to recognise the key features of a piece of student work. The teacher candidates' responses to the tasks highlighted the diverse nature of the prior knowledge that underpinned their responses. The study raises questions about the pedagogy of initial teacher education, particularly in relation to the assumptions teachers educators make about the candidates they teach. The findings suggest that the prior knowledge that students bring to initial teacher education is both a resource and a challenge for teacher educators. (Contains 1 figure and 3 tables.)