In this study, we juxtapose the purpose and procedures for school science inquiry activities as they are portrayed in curriculum policy statements, provincial assessment materials and teacher resources with a teacher's enactment of these policy and resource directives in her classroom. This article draws on data collected during a Grade 6 classroom inquiry into evidence supporting the existence of air. Data consist of field notes taken during observations in a sequence of five lessons and transcripts of audiotaped lessons and teacher interviews. Guided by the questions 'How is science inquiry shaped through a discourse of policy statements and teacher resources?' and 'How is science inquiry mediated by instructional discourse?', we explore the discourses in which school science is embedded. The findings suggest that an institutional discourse of accountability dominates the instructional discourse and confines an orientation to inquiry.