There has been increasing concern about the presence of disengaged test taking in international assessment programmes and its implications for the validity of inferences made regarding a country's level of educational attainment. This issue has received a growing research interest over the past 20 years, with notable advances in both the measurement of disengagement as well as our understanding of its distortive impact on both individual and aggregated scores. In this paper, I discuss six important insights yielded by this research and their implications for assessment programmes.