Despite the increase in teaching approaches designed to integrate sustainability into higher education, the connection between students' learning experiences and their learning outcomes remains incompletely understood. The present multi-case study complements the discussion by investigating undergraduates' long-term meaning-making processes using the theoretical lens of significant learning and process analysis of students' learning experience. Based on in-depth narrative interviews with 10 students at the end of a three-year study program, we analyzed how and why learning experiences become significant, differentiating perceived personal impact and the subjective value assigned to these experiences. We identified three types of sustainability-related meaning-making processes, ranging from "no sustainability-related meaning-making" to "meaning-making as self-realization." The differentiated view on how meaning-making mediates students' sustainability-related learning experiences and their learning outcomes enhances our understanding of the specific dynamics that may shape the how and why of significant learning. It thus supports the tailored curriculum design for integrating sustainability into higher education.