Recent studies have emphasized the growing relevance of portfolios in higher education, particularly as a tool that fosters reflective and formative assessment practices. This article presents a qualitative study conducted with a group of Education students, exploring the portfolio as the primary assessment method. The research investigates the conditions under which portfolios can serve as effective tools for both self and peer assessment, using reflective cognition (metacognition) to enhance learning. Classroom observations were combined with open-ended questionnaires, and data analysis was conducted using webQDA software to ensure rigor and objectivity in interpreting the findings. The study reveals that the use of portfolios not only fostered student agency and autonomy but also strengthened self-responsibility and promoted deeper engagement with the learning process. Furthermore, portfolios facilitated a more dynamic, transparent, and collaborative relationship between students and instructors, offering a structured yet flexible approach to assessment. By aligning with competency-based curricula, the portfolio enables a more personalized and meaningful evaluation of students' development, shifting away from traditional, static assessment models. This study contributes to the advancement of assessment practices in higher education, advocating for portfolios as a critical tool in promoting cognitive development, reflexive thinking, and an integrated approach to learning and assessment.