As the author demonstrates, whenever preservice or beginning teachers observe a veteran teacher in action, the veteran serves as a mentor, in the sense that the experienced teacher is modeling the practices that can influence the newcomer. In this article, the author reminds educators about the importance of formative assessments, not just of the students' learning but also of the teacher's effort to provide the best instruction possible. The author stresses that those who direct the preparation of new teachers or who serve as mentors for newcomers within the schools, it is important that the mentor's actions remain consistent with the practices that the mentor recommends: In short, they must practice what they preach. The author describes here two practical structures that can serve the teacher as reflective practitioner and that can model for new teachers how they can take the measure of the effect of their instructional efforts. (Contains 1 note.)