Dynamic and responsive methods enable teachers to assess students' writing skills precisely and equitably, and to empower students of diverse skill levels to develop their writing. Assessing writing with equity-minded precision requires paying close attention to students' performances as writers, identifying challenges in those performances, and providing customized support. The authors propose that the practice of skilled formative writing assessment entails the performance of three distinct roles: "reader," in which the teacher expresses an understanding of the student text, often reflecting or "saying back" their understanding; "assessor," in which the teacher either evaluates the text or asks a diagnostic question; and "instructor," in which the teacher provides support intended to enable the student to solve a problem or overcome a challenge. The authors offer three brief examples from our research on actual teacher-student dialogic assessment sessions, conducted by teachers working in public high schools in or near a large metropolitan school district in the Northeastern United States.