As interest in improving the quality of teaching has increased, so has an interest in how teachers can be mentored. We described the Practice of one mentor as she assisted three beginning teachers to shift their teaching practice to a more robust understanding of the high-leverage practice of discussion-based teaching. This mentor participated in a two-year university-led professional development intervention to prepare her to target discussions as a focus. Tenets of assisted performance are used to analyze the mentoring approach used with each unique beginning teacher. The tenets of assisted performance include: (a) identifying performance levels, (b) structuring situations, and (c) scaffolding support and preparing for unassisted performance. In this study, we documented ways in which the mentor demonstrated authority to persist in moving each beginner to embrace features of a complex practice related to reform-based teaching.