Soft skills have become a subject of increasing interest in lifelong learning. Soft skills development is intended to enable and enhance personal development, participation in learning and success in employment. The assessment of soft skill is therefore widely practised, but there is little in the way of research or evidence on how well this assessment is done. Critically reviewing soft skills assessment requires both theory development and establishing a research agenda. Theory development can draw on a number of established theories which help to explain how the cognitive, emotional and social dimensions interact to shape learner behaviour around getting feedback. These include control theory, goal theory and attribution theory. Theory development following an assimilative integration approach based on attribution theory, which combines both "self-regulation" and "socially situated" aspects, is suggested as the most fruitful. Three areas of research can be associated with this; researching the context, the content and the consequences of soft skill assessment. The challenges of this research agenda are outlined and explored. Dealing with these challenges will enable a more robust and critical review of the assessment of soft skill, and the impact of that on both life chances and employment opportunities.