Grounded in Vygotskian sociocultural theory (SCT), this study examines Korean as a foreign language (KFL) students’ emerging conceptual development of honorifics through their participation in concept-based language instruction (C-BLI). Seven participants were recruited from a second-semester elementary Korean class at a U.S. college, and various data were collected to trace the students’ unfolding development-in-activity of three interrelated subconcepts of Korean honorifics; namely, power, distance, and formality. Qualitative findings suggest that, overall, students gained a deeper conceptual understanding and sociopragmatic awareness of using Korean honorifics through the development of these interrelated subconcepts and their participation in the goal-directed activities of C-BLI. In particular, the qualitative findings reveal that students’ prior rules-of-thumb-based conceptualizations of honorifics transformed into more semantic, systematic, coherent, and complete understandings as students are in the process of becoming more self-regulated in planning and monitoring their mental and physical activity and their linguistic choices. This study points to the crucial importance of not only the quality of materials design but also how intentional and explicit instruction can be applied to second language teaching–learning processes.