Teachers spend a substantial amount of their work time on assessment, yet school assessment processes and practices continue to be an area characterised as “a problem.” The supposed problem comes into stark relief when considered against the moves by governments internationally towards large-scale testing for comparative reporting purposes, and the development of school testing corporations. Nevertheless, it is widely recognised in education research, policy, and practice that assessment can and should be used to improve, not just to report, student learning. Also recognised is that increasing emphasis on accountability policies around the world carries potentially negative consequences for teaching and assessment practices. Research has shown that school leaders play a critical role in responding to accountability pressures through development of school policies and practices that ensure assessment evidence will be used to improve student learning. Further, leadership in assessment and developing an assessment culture must be shared activity if ongoing change is to occur in practice. We outline three stages, distilled from research, that translate the rhetoric of effective leadership in assessment into developing an assessment for learning culture in the school: developing a school policy for managing student assessment to support learning; building a positive and constructive learning culture within the school; and encouraging a broad range of learning activities and learning outcomes. We provide practical direction for essential components of these stages.