The purpose of this research was to reflect on how peer-assessment in higher education can enhance critical thinking and learning. In this paper, we will focus on a specific case study; a peer-assessment process organised for a drawing unit in the School of Architecture, University of Portsmouth. The students assessed their colleagues’ drawing portfolios; the body of work that had been created throughout the semester and then submitted for examination. Through this paper I will present the reasons for which the peer-assessment was introduced, how the peer-assessment process was organised, what difficulties and potential benefits emerged, and how students responded to it. One of the main observations was that after the marks moderation carried out by the tutors 93% of the marks did not change. Only 7% of the marks for the drawing portfolios were modified. In this paper I examine this 7% further; I observe the peculiarities of these particular portfolios and the reasons for which the students were having difficulties marking them.