Vygotsky’s notion of a zone of proximal development (ZPD) forms the basis of this methodologically oriented chapter’s approach to the analysis of response dialogues in education. The first part presents a theoretical framework where the focus on zones of proximal writing development is 1) anchored in Vygotsky’s understanding of the relations between development, learning and teaching; 2) methodologically elaborated by a Bakhtinian understanding of utterance and chain of utterances and 3) educationally justified as an expedient tool for a Bildung-oriented teaching of writing. The second part illustrates how zones of proximal writing development may be documented through analyses of text response dialogues between students and teachers. The examples used come from two empirical studies: a case study of a writing process where a teacher commented on first drafts written on paper by her twenty students, and an ethnographical study over three years of literacy practices in newly digitalized classrooms, including online teacher–student dialogues about texts in the making. The analytical examples highlighted here focus on the mediation of a text pattern that was increasingly mastered by one of the students in the first study, and digital teacher–student dialogues in a ‘possibility room’ that was opened in the document margins of emerging texts in the second study. In the concluding part, methodological and educational implications of the proposed and illustrated approach to zones of proximal writing development are discussed.