The author argues that assessment in education has become over-conceptualised and overcomplicated, and assessment concepts and terminology introduced over the past half century sometimes now function as impediments to clear thinking and good practice. The one fundamental purpose of assessment in education, he says, is to establish and understand where learners are in an aspect of their learning at the time of assessment. When this is recognised, many supposedly important distinctions become less significant. Currently, however, such distinctions tend to result in fragmentation of the field, with proponents championing one assessment purpose or method while denigrating others. He explains why advances in assessment theory and practice require a more unified conceptualisation.