This article considers issues in educational reform, particularly accountability-oriented policies, and student motivation. We argue that prominent theories of motivation derived from cognitive traits/states are antithetical to the assumptions underlying conventional assessment formats and accountability-oriented reforms. We advance an alternative perspective that emerges from sociocultural assumptions. In this perspective, the values and beliefs that motivate engagement in learning reside alongside the practices that characterize knowledge communities and, together, constitute a model of practice. We therefore explore the complex issue of reconciliation between the activities of individuals and social contexts and how "dialectical" reconciliation addresses tensions between classroom assessment and external testing, and between formative and summative functions of assessment. Data and conclusions from a program of research in science education illustrate and warrant these considerations.