The theory of formative assessment outlined in this article is relevant to a broad spectrum of learning outcomes in a wide variety of subjects. Specifically, it applies wherever multiple criteria are used in making judgments about the quality of student responses. The theory has less relevance for outcomes in which student responses may be assessed simply as correct or incorrect. Feedback is defined in a particular way to highlight its function in formative assessment. This definition differs in several significant respects from that traditionally found in educational research. Three conditions for effective feedback are then identified and their implications discussed. A key premise is that for students to be able to improve, they must develop the capacity to monitor the quality of their own work during actual production. This in turn requires that students possess an appreciation of what high quality work is, that they have the evaluative skill necessary for them to compare with some objectivity the quality of what they are producing in relation to the higher standard, and that they develop a store of tactics or moves which can be drawn upon to modify their own work. It is argued that these skills can be developed by providing direct authentic evaluative experience for students. Instructional systems which do not make explicit provision for the acquisition of evaluative expertise are deficient, because they set up artificial but potentially removable performance ceilings for students.