Long-standing concerns within the field of educational assessment consider the impact of assessment policy and practice as matters of equity, inequality and social justice. Yet educational assessment policy and practice continues to have powerful social consequences for key users such as children and young people. This paper re-positions these consequences as a matter of ethics. It uses the work of Messick to frame how ethical matters extend beyond test instruments into the realm of uses and impact. A case study of the 11+ school transfer system in Northern Ireland is presented to illustrate ethical dilemmas emerging as a consequence of actions and decisions of using assessment systems for particular purposes. In looking forward to how we might attend to ethical matters in assessment policy and practice, a consideration of a children's rights approach is outlined that may provide a moral and legal framework for action. (Contains 2 tables and 2 notes.)