The purpose of this study was to compare the effects of social media language learning activities with traditional language learning activities on the development of L2 grammatical competence in two English as a Foreign Language (EFL) classes at a Taiwanese university. The study was grounded in four bodies of knowledge: (a) the Input-Interaction-Output (IIO) model (Block, 2003); (b) the sociocultural/activity theory (Lantolf, 2000); (c) current L2 grammar learning theory (Ellis, 2006); and (d) computer-assisted language learning (CALL) theory (Levy & Stockwell, 2006). A convenience sample of 84 Taiwanese undergraduate students officially enrolled in the college voluntarily participated in the study. A quasi-experimental pretest/posttest design was utilized. An ANCOVA was conducted to assess whether collaborative social media activities can bring about significantly better outcomes regarding EFL grammar usage. Results indicated that the treatment group significantly outperformed the control group when controlling for pre-existing knowledge. Results also indicated that there was a significant difference in students' time devoted to English grammar activities between the treatment group and the control group in favor of the treatment group. Furthermore, there was a statistically significant relationship between the time spent on wiki sites and students' English grammar achievement gains. The time students in the treatment group spent on grammar activities increased when they used the social media, and they self-reported spending more time on task during free time. Overall, treatment group students' devotion to the social media activities brought about effective peer support and collaborative learning. [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.]