The purpose of this qualitative action research study was to explore improving first semester training practices for graduate teaching assistants (TAs) in the Spanish program at Arizona State University's (ASU) Tempe Campus. Adding to research on TA training in higher education, a communities of practice (CoP) framework was combined with concrete suggestions on cultivating CoPs to implement a two-part CoP principled training program intervention. Specifically, a goal of the intervention was to address the problem of practice of improving first semester TA lesson planning, communicative language teaching, classroom management, and learning management system usage. Data was collected from interviews, surveys, journals, and training activities from five new TAs who teach Spanish. Data analysis included a multi-cycle qualitative coding process to examine participants' novice-expert positionalities and the presence of core features of a CoP. Results suggest that regardless of previous experiences, TAs need time to assimilate to the ASU culture, standards, and community. Furthermore, the CoP principled training program showed instances of the necessary core features of a CoP such as joint enterprise and mutual engagement, but also a need for continued community development to address dysfunctions. Implications for these findings point to possible positive effects of continued training through a CoP framework, and a need for reorganization of training practices to allow TAs to legitimately participate in training activities supported by community coordinators as they adjust to the ASU context before beginning their in-service teaching. [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.]