Formative assessment is intended to develop students' capacity to learn and increase the effectiveness of teaching. However, the extent to which formative assessment can meet these aims depends on the relationship between its conception and current conceptions of learning. In recent years concern about sex group differences in achievement has led to policy directives that have required English teachers to reconsider their curriculum and their practice. Ameliorating strategies such as single-sex groupings and gendered seating are based on common-sense beliefs about gender rather than research. Case-study data are used to examine the consequences of these strategies for students' literacy learning by exemplifying how settings influence the dynamic construction of knowledge, and how knowledge and, therefore, what is assessed, is legitimated by teachers. Socio-cultural approaches to learning challenge dominant conceptions of formative assessment and highlight that classroom practices are at once situated and mediated by processes beyond the school. (Contains 1 table.)