The study documented the dynamic process of designing and implementing instructional interventions in an online course of Japanese language and culture at a two-year college. The results have impact in three distinct areas: pedagogical, theoretical, and methodological. First, the interventions that encouraged student agency with rich contextualization were designed for students to become able to use Japanese in real life. The results suggested that how students were engaged in the class activities as well as how the design itself influenced their second language (L2) learning. Second, the study challenged the issue that previous empirical research on online L2 learning was primarily conducted based on information-processing theories that could only reveal a part of L2 learning, limited to linguistic acquisition. Using sociocultural approaches, this study demonstrated how the authentic contextualization and students' agency in the interventions augmented their L2 developmental potentials, which was not limited to linguistics but expanded to include pragmatics, sociocultural knowledge and meta-cognitive awareness. Third, the methodology of formative and design experiments suggested the importance of analyzing every factor that might affect students' learning in uncontrolled natural educational settings. This study portrayed the dynamic interactional nature of the elements in the educational environment, such as the teacher, students, and the interventions. Unlike laboratory-based studies that focus upon only limited variables, the study captured that the very process of analysis unfolded reality in a different way, which eventually resulted in bridging the discrepancy between theory and practice. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]