This qualitative case study examines learners' experiences in the development of written complexities during Discussion Board (DB) assignments in an Advanced university level Chinese class. Discussion Board was chosen as the avenue for written complexity development because it provides learners a supplementary space with additional time and opportunities for low anxiety writing. The data collection for this study came from two sources, DB posts and interviews. This study seeks to fill gap in the literature in two ways: one, this study proposes a measurement of written complexities that consists of propositional complexity, lexical sophistication and accuracy. Second, this study highlights student experiences and explores the learning process from their perspectives. Using Vygotsky's (1978) Sociocultural theory as theoretical framework, the findings of this study generated new knowledge about what tools and strategies Chinese as a Foreign Language (CFL) learners used to develop written complexities during the DB discussion activities. Additionally, this study examined how CFL learners utilized DB activities and interactions on DB to develop written complexities. Finally, this study demonstrates how DB can serve as a supplementary learning space, where if designed appropriately, can lead to opportunities for students to develop their written complexities. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]