Co-assessment is a type of participatory assessment in which the teacher and student jointly discuss, negotiate and assess the student's task or performance. Although the literature on co-assessment is scarce, some authors highlight the benefits for students of participating in co-assessment in higher education, including learning, improved communication, and greater assessment literacy. This study has a double objective: on the one hand, to analyse the strengths and limitations perceived by students participating in co-assessment practices; on the other hand, to explore the strengths, weaknesses, opportunities and threats perceived by professors participating in the experience. The study was developed in 8 class groups with the participation of 470 students and 4 teachers. The qualitative analysis of the data obtained from the questionnaires and focus groups indicates that the students acknowledged several strengths, among which learning from mistakes was prominent. Students also noted some limitations, particularly the lack of adjusted scoring. Professors offered another perspective that complemented the vision of their students, noting that co-assessment presents opportunities as well as risks that may jeopardise its implementation.