This paper set out to explore teachers' narratives in order to understand some of the facilitators and constraints which promote or inhibit good formative assessment practices in schools. A "responsive interview" approach was used to probe a small sample of lower and middle school teachers' perceptions of formative assessment. Qualitative thematic analysis of data identified four key themes which had important implications for pedagogical practice. These were: prescription and ownership; accountability; school context, culture and collaboration; and leadership and management. Evidence from this study suggests that, while teachers may recognise the value of formative assessment in promoting learning, conflicts and tensions between government policies and school practices may inhibit its effectiveness.