This paper explores the developing thinking about assessment of graduate trainees preparing for secondary teaching in England. For some years teachers in English schools have worked in a context where the outcomes of formal testing have been used to judge school and teacher performance as well as student achievement. Research evidence that formative modes of assessment contribute more to student learning has in recent years led to strong recommendations that most classroom assessment should be "Assessment for Learning" (AfL). In reality the new orthodoxy of AfL is being championed in a context where high-stakes testing retains its perceived role in ensuring "accountability". Interviews with a sample of trainee teachers at an early stage of preparation for teaching suggest that their preconceptions about the nature and purpose of assessment, and their interpretations of classroom observations on school placement, offer a confused and complex basis for adopting recommended assessment practices in their own teaching. (Contains 1 table.)