Traditional assessment practices in higher education often emphasize outcomes while neglecting the learning process and the development of reflective and professional competencies. This limitation underscores the need for more authentic, process-oriented evaluation methods. The purpose of this study was to investigate the effectiveness of portfolio assessment in the course Linguodidactic Basis of Professional Activity of a Foreign Language Teacher at a Kazakhstani university, with a focus on how portfolios influence engagement, reflective learning, and the integration of theory into teaching practice. A qualitative case-study design, supported by descriptive quantitative analysis, was employed. The participants were 28 undergraduate students and two instructors. Data were collected from semi-structured interviews, portfolio artifacts, and rubric-based portfolio scores. The results of thematic analysis revealed four primary outcomes: (1) enhanced engagement and ownership of learning, (2) growth in reflective and metacognitive skills, (3) authentic application of theoretical knowledge in teaching practice, and (4) challenges related to time management and workload. Quantitative analysis showed that portfolio scores ranged from 64% to 98% (M = 86%, SD = 8.2), with the highest results in developing teaching materials and the lowest in monitoring and evaluating learners. The key conclusion is that portfolio assessment supports constructive alignment between learning outcomes and competencies, fosters pedagogical reasoning, and promotes professional development. At the same time, variability in reflection depth and instructor workload highlights the need for additional scaffolding and support. Overall, the findings confirm that structured, criteria-based portfolios represent a practical and comprehensive tool for authentic assessment in teacher education.