Context Conceptualisations of self-assessment are changing as its role in professional development comes to be viewed more broadly as needing to be both externally and internally informed through activities that enable access to and the interpretation and integration of data from external sources. Education programmes use various activities to promote learners' reflection and self-direction, yet we know little about how effective these activities are in 'informing' learners' self-assessments. Objectives This study aimed to increase understanding of the specific ways in which undergraduate and postgraduate learners used learning and assessment activities to inform self-assessments of their clinical performance. Methods We conducted an international qualitative study using focus groups and drawing on principles of grounded theory. We recruited volunteer participants from three undergraduate and two postgraduate programmes using structured self-assessment activities (e.g. portfolios). We asked learners to describe their perceptions of and experiences with formal and informal activities intended to inform self-assessment. We conducted analysis as a team using a constant comparative process. Results Eighty-five learners (53 undergraduate, 32 postgraduate) participated in 10 focus groups. Two main findings emerged. Firstly, the perceived effectiveness of formal and informal assessment activities in informing self-assessment appeared to be both person- and context-specific. No curricular activities were considered to be generally effective or ineffective. However, the availability of high-quality performance data and standards was thought to increase the effectiveness of an activity in informing self-assessment. Secondly, the fostering and informing of self-assessment was believed to require credible and engaged supervisors. Conclusions Several contextual and personal conditions consistently influenced learners' perceptions of the extent to which assessment activities were useful in informing self-assessments of performance. Although learners are not guaranteed to be accurate in their perceptions of which factors influence their efforts to improve performance, their perceptions must be taken into account; assessment strategies that are perceived as providing untrustworthy information can be anticipated to have negligible impact.