In an effort to gain better understanding of the assessment of prior informal and non-formal learning, this article explores assessors' approaches to portfolio assessment. Through this portfolio assessment, candidates had requested exemptions from specific courses within an educational programme or admission to the programme based on their prior learning. The assessors judged the portfolios according to set rating criteria, and subsequently discussed their approaches. Their decision-making processes, perception of portfolio use in the Assessment of Prior Learning (APL), deciding factors in portfolio assessment and use of the rating criteria were key elements in this discussion. The results show that they do use the rating criteria as an indicator in decision-making, but have mixed perceptions regarding the fairness of APL portfolio assessment. They perceive the portfolio evidence in combination with sound argumentation as the deciding elements in portfolio assessment. [ABSTRACT FROM AUTHOR]