Introduction Portfolio-based assessments require that learners’ competence development is adequately reflected in portfolio documentation. This study explored how students select and document performance data in their portfolios and how they perceive these data to be representative for their competence development.

Methods Students uploaded performance data in a competency-based portfolio. During one clerkship period, twelve students also recorded an audio diary in which they reflected on experiences and feedback that they perceived to be indicants of their competence development. Afterwards, these students were interviewed to explore the extent to which the performance documentation in the portfolio corresponded with what they considered illustrative evidence of their development. The interviews were analyzed using thematic analysis.

Results Portfolios provide an accurate but fragmented picture of student development. Portfolio documentation was influenced by tensions between learning and assessment, student beliefs about the goal of portfolios, student performance evaluation strategies, the learning environment and portfolio structure.

Discussion This study confirms the importance of taking student perceptions into account when implementing a competency-based portfolio. Students would benefit from coaching on how to select meaningful experiences and performance data for documentation in their portfolios. Flexibility in portfolio structure and requirements is essential to ensure optimal fit between students’ experienced competence development and portfolio content.