Many medical courses use standards-based assessment, usually reported by a restricted range of categories, but there is little evidence of its educational impact. This study aimed to evaluate the impact on medical student learning of changing to standards-based assessments reported by distinction, pass or fail. We carried out a prospectively planned before-and-after study within an undergraduate medical course using a questionnaire to compare motivation and approaches to the study, and a diary to compare the number of hours spent studying. The changes were associated with beneficial effects on deep motive, deep strategy, professional identify and intrinsically motivated study. There were no changes in competitiveness and minimal changes in amount of time spent studying.