Research shows that effective and high-quality instructional coaching that targets teacher-child interactions can improve the classroom quality, increase teacher job satisfaction, reduce attrition, and even improve young children's development, such as social emotional development, and literacy skills. Coaches likely develop and sharpen their communication, leadership, coaching, and reflective skills, as well as their sense of professional identity over time. Thus, the current study uses data gathered from instructional coaches and their preservice teachers (PSTs) during their internships to explore (1) the dynamic process of how coaches develop their professional competency in an empirically validated coaching program, and (2) the elements of high-quality, effective coaching with PSTs. After analyzing transcriptions of two interviews with 11 instructional coaches, four themes were found that supported the MMCI Coach's Professional Competency Development: Deepened understanding of the Teaching through Interactions Framework, Increased sense of professional identity, Sharpened coaching skills, and Enhanced mentor--mentee relationships.