CONTEXT: In health professions education, assessment systems are bound to be rife with tensions as they must fulfil formative and summative assessment purposes, be efficient and effective, and meet the needs of learners and education institutes, as well as those of patients and health care organisations. The way we respond to these tensions determines the fate of assessment practices and reform. In this study, we argue that traditional 'fix-the-problem' approaches (i.e. either-or solutions) are generally inadequate and that we need alternative strategies to help us further understand, accept and actually engage with the multiple recurring tensions in assessment programmes. METHODS: Drawing from research in organisation science and health care, we outline how the Polarity Thinking™ model and its 'both-and' approach offer ways to systematically leverage assessment tensions as opportunities to drive improvement, rather than as intractable problems. In reviewing the assessment literature, we highlight and discuss exemplars of specific assessment polarities and tensions in educational settings. Using key concepts and principles of the Polarity Thinking™ model, and two examples of common tensions in assessment design, we describe how the model can be applied in a stepwise approach to the management of key polarities in assessment. DISCUSSION: Assessment polarities and tensions are likely to surface with the continued rise of complexity and change in education and health care organisations. With increasing pressures of accountability in times of stretched resources, assessment tensions and dilemmas will become more pronounced. We propose to add to our repertoire of strategies for managing key dilemmas in education and assessment design through the adoption of the polarity framework. Its 'both-and' approach may advance our efforts to transform assessment systems to meet complex 21st century education, health and health care needs.