This study aimed to investigate how students' conceptions of assessment relate to one another, how students define assessment, and how student conceptions of assessment relate to their definitions of assessment. A nationally representative sample of New Zealand secondary students (N = 705) responded to a 45-item Conceptions of Assessment inventory and a list of 12 assessment practices. Well-fitting measurement models were found. The more students agreed that assessment was to help them improve the more they associated assessment with teacher-controlled practices. Further, the more students perceived assessment as irrelevant the more they defined it as interactive-informal practices. Thus, more student-oriented practices were conceived as creating a positive social environment that was irrelevant to learning. (Contains 1 table and 5 figures.)