Within the paradigm of Sociocultural Theory, and using Activity Theory as a data-gathering and management tool, this microgenetic case study examined the processes--the growth, change, and development--engaged in by student-teachers in a foreign language education program as they worked together to complete an activity. The activity involved digital video recording and editing, mediators which were intended to facilitate the iterative review of and subsequent reflection and action upon the content of the video during its creation. By investigating the process of contextual interaction between learners and the mediational elements of their environment as the activity progressed, this study intended to further understanding of preservice teacher development in at least two important ways. The aims of this study were to discover (a) tangible evidence of cognitive transformation (development in the form of regulation), as well as (b) aspects of professionalization into a community of skilled second language teachers (as evidenced by activity). The present study took place in a graduate-level foreign language/TESOL education practicum course. The activity involved the making of a digital video to explain and exemplify a given second language instructional approach, as well as the rationale behind and methods of targeting a specific language skill. Using theoretical constructs previously shown to be effective in the pedagogy of teacher preparation, the creators of this task endeavored to design a socially- and artifact-mediated activity with the potential to broaden and deepen student-teachers' pedagogical and professional knowledge. The student-teachers failed to engage in meaningful dialogical or critical reflection as they engaged in the task, and made no perceptible regulative movement. What ultimately was revealed in the case of the study participants was a disconnect between the intentions of the core-task designers and the outcomes effected by the student-teachers. The data gleaned from this close examination of student-teacher processes was revelatory in terms of the quantity and types of factors that appeared to significantly impact the outcomes of the project. These factors have the potential to inform the process of translating socio-cultural theory into pedagogical practice, and may be of interest to anyone involved in the development of student-teachers, including those who design or deliver preservice teacher curricula. Discussed are the possible explanations for the disconnect between the designers and administrators of the activity and the participants in the study. Also considered are the implications for second language teacher education programs and their curricula in terms of the application of socio-cultural constructs to learning tasks and environments. Recommendations include increased scaffolding by the course professor through direct guidance, as well as by structuring tasks to facilitate students' ability to collaborate and to perceive and resolve the conflicts, contradictions, and tensions that arise during the course of the activity. [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.]