The dissertation examines how synchronous text-based computer-mediated communication (SCMC) tasks may affect English as a Second Language (ESL) learners' development of second language (L2) and academic literacy. The study is motivated by two issues concerning the use of SCMC tasks in L2 writing classes. First, although some of the alleged benefits of SCMC, including its visual saliency and the possibility of slower processing speed, have been supported by theories of Second Language Acquisition (SLA), more evidence is still needed since empirical studies have not yet produced enough consistent findings. Second, most studies on SCMC have focused on its influence on learners' development of basic communicative competence while it has been suggested that SCMC may hold great potential for the development of advanced academic literacy (Luo, 2005; Mohan & Luo, 2005) that is considered as an essential goal for L2 writing classes. Therefore, the dissertation addresses these issues using mixed methods research completed in two phases. A quasi-experiment was conducted in the first phase among forty-four international students enrolled in two sections of an ESL academic writing course to examine the differential effects of SCMC and face-to-face tasks. The differential effects were assessed by comparing the students' improvement on measures of L2 grammatical and lexical complexity, accuracy, and fluency (Wolfe-Quintero, Inagaki, & Kim, 1998) from a pre-test to a post-test. The results of the quasi-experiment were also used to help select representative focal students for the multiple case studies in the second phase where the SCMC discourse of the focal students was examined for the details of L2 learning and the development of academic literacy. In analyzing the SCMC discourse of different triads, instances of L2 learning opportunities based on the Interaction approach and sociocultural theory of L2 learning were identified and classified, and the patterns of learning for each triad and between triads were discussed. The SCMC discourse was then re-analyzed to examine how the focal students developed their ability to construct effective arguments by participating in the back-and-forth rhetoric and by learning to use meta-discourse devices appropriately. The patterns of learning observed in the SCMC discourse of the focal students were also compared with the patterns observed from their writing samples. The quasi-experiment and the multiple case studies were connected by a mixed methods research design (Creswell & Plano Clark, 2007, p. 73) whose aim was to understand how SCMC tasks might affect both the outcome and the processes of the development of L2 and academic literacy. The results largely confirmed the benefits of SCMC tasks on L2 written accuracy and fluency, and suggested that SCMC tasks had great positive potential in engaging students in the processes of arguments to help them learn to incorporate discussions of opposing views in building effective arguments. Future research may further examine the differences of learning between pairs, triads, or small groups working on the same SCMC task. Research on the use of SCMC tasks and the learning of meta-discourse devices can also inform pedagogical decisions. [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.]