Assessment is a major component of education, significant in directing what is identified as valued student learning. This paper is framed within an understanding of imperative and exhortative policy. Two paradigmatically different, and potentially contesting, assessment policy directions in Australian education -- educational accountability to monitor school and teacher performance, and teacher assessment practices to improve learning (assessment for learning [AfL] or formative assessment) -- are examined for their impact on teacher professionalism. Both approaches have official endorsement in Australian policy. Mandated participation in national tests is indicative of educational accountability assessments under national direction. While also endorsed nationally, AfL implementation is reliant on state and territory direction. Our examination reveals tensions in the alignment of both policies. This is evident in the impact of accountability assessment on AfL implementation, in particular, teachers' understandings of valued assessment evidence. We conclude that a paradigmatic shift to support student learning in Australian schools is a policy imperative that includes the need for professional development and learning support for teachers.