Taking sociocultural theory (SCT) as a theoretical framework, this qualitative phenomenological case study investigated the mediational discourse of a series of ten observation and post-observation conferences between a coach and an English language teacher teaching at Iran Language Institute (ILI) in Shiraz, Iran, in order to represent the development of student-focused oral feedback in an EFL teacher over time. Features of verbal mediation already identified by Wertsch (1998) such as shared definition of the task, inter-subjectivity, graduated help, and reasoning existed in the data, while they were insufficient in triggering the teacher to think conceptually about his use of oral feedback to students. Similarly, professional discourse, languaging motives, and teacher dynamicity, alongside the aforementioned meditational features, were revealed to be pivotal on the uptake of conceptual thinking by the teacher. The study was divided into three phases, namely, before, during, and after verbal mediations given by the coach to the teacher participant. The results of the study, along with the previous descriptive and empirical studies, accounted for an obvious role of mediational discourse in the development of teacher’s understanding of conceptual thinking through verbally-mediated activity. The results also found that negotiated help given by the teacher to learners was excessively pivotal in assisting learners to internalize their oral errors. The study concluded with some pedagogical implications for second language teachers to be reflective, dynamic, and evaluative in dealing with oral corrective feedback challenges in their classroom practices.