International teaching assistants (ITA's) perform a variety of instructional roles in undergraduate education within North American universities. ITA training programs often exist to prepare them for such roles. Empirical work has examined ITA training courses, but most often through the practitioner's lens of program evaluation, which obscures many of subtleties of ITA's development. Most of this work focuses only on In-Service ITA's, the enrolled ITA's who concurrently serve in an instructional role for an undergraduate classroom. This narrowed focus excludes from much of the literature the perspectives of Pre-Service ITA's. More problematic is that undergirding much of the empirical ITA literature is the assumption that ITA's are wholly motivated to develop their skills because of their immediate need for such skills as instructors. Based on this assumption, the ITA's experience of the ITA training class has been largely overlooked. Like all second language learners, ITA's have complex motivations, identities, and learning trajectories that can fluctuate during their learning. These aspects need to be better understood. Should such areas remain unexplored, our understanding would remain limited to the outcomes of an ITA Training class, rather than the processes involved in it. What would result would be a misunderstanding based upon inaccurate assumptions. Pedagogies developed using these assumptions could impact not only the ITA learners, but the undergraduate students who ultimately receive instruction from ITA's. To address these shortcomings in the literature, a descriptive, qualitative, multiple case study was conducted during a semester-long ITA training course at Paw Paw State University (PPSU, pseudonym), a large research university in the American Midwest. To examine ITA's experience in the class, the study examined the ITA's investment (Norton & Darvin, 2015), which accounts for learners' identity, capital, and the ideological dimensions. It also studied their perspectives on plagiarism and L2 Transfer Motivation. Also explored were the ideologies of the instructors who taught the ITA training course, and those of the home departments in which the ITA participants were studying. A total of 6 ITA participants (3 Pre-Service and 3 In-Service ITA's) were enrolled in 3 different sections of the same Spoken English course during the Autumn 2018 semester, taught by 3 different instructors. Data was collected through ITA's weekly journals, individual interviews and stimulated recalls, class assignments, and classroom observations of the ITA training class and home department courses. Data was also collected from instructors and home departments through interviews. Analysis of the data was done in conformity with standards of interpretive, qualitative SLA research. It was found that the most significant difference between the investment of ITA's within ESL 9999 did not stem from the distinction between being a Pre-Service or an In-Service ITA. Rather, most salient was the section type of ESL 9999, being either test centric or non-test centric. Additionally, it was found that investment was shaped in large part by home department policies, by the instructors' pedagogies, and by exposure to teaching role models. Specific cases revealed insights into how ideologies converge in defense of a learner's identity, and how ideologies can bring two learners to polar-opposite assessments of their experiences in a singular ESL 9999. A clearer picture of L2 Transfer Motivation also emerged. Implications from this study will benefit SLA theorists, ITA professionals and curricula, hopefully ITA's themselves, and ultimately the undergraduate students they teach. [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.]