To become effective teachers of Teaching English to Speakers of Other Languages (TESOL), developing an extensive knowledge base about language and about language learning/teaching is essential. In graduate TESOL programs, second language teacher educators often devise authentic teaching opportunities for pre-service teachers (PSTs); however, these teaching experiences tend to occur in the later stages of graduate training. The goal of the present study was to examine the affordances of introducing a planned tutoring program during the first semester of a graduate TESOL program on PSTs' developing knowledge base. During the final weeks of a teaching methodology course, 13 PSTs were each paired with an English as an Additional Language (EAL) learner and enacted teaching in a safe environment while receiving guidance from their instructor. Drawing on Vygotskian-inspired theoretical concepts, a qualitative analysis of the participants' post-teaching reflections and of their portfolio (lesson plans, materials, instructor feedback) revealed how they applied, shaped, and transformed their understanding of pedagogical concepts.