Assessment for learning has been widely reported as a reform in educational assessment. The recently published OECD study (OECD, 2005) provided several case study investigations of how assessment for learning is variously enacted in diverse policy and system contexts. In this paper we take up the topic of assessment for learning and draw on a recently completed large-scale study of teacher capacity-building in assessment in middle schooling (Years 4 to 9; ages 8 to 14 approx.) to explore characteristics of 'assessment as critical inquiry'. Specifically, we probe the question, How can we enact a framework of assessment as critical inquiry for improving learning outcomes? The paper proposes a conceptual framing for developing a professional mindset that places assessment at the heart of the pedagogic enterprise.