This paper reports on a year-long research study: four teachers of English, their Year 8 (13-14 year old) classes (110 students) in urban, secondary schools and a university teacher educator investigated the contexts for students to develop dialogic, exploratory talk in small groups. Assuming a Vygotskyan perspective, the study adapted a pedagogic model from an earlier project, endorsing a structured approach to talk, with "ground-rules" and reflection. The study investigated how this guided model might intersect with other aspects of classroom culture, practice and identity to effect sustained development in students' use of exploratory, dialogic talk. The project involved research collaboration cross-school, including students exchanging formative feedback on videotaped talk. Qualitative research methods comprised comparative discourse analysis of audio and videotapes of representative group talk; semi-structured lesson observations; and sequential teacher and student interviews. The study concludes that practising a structured model and reflecting on discourse had a liberating effect on the majority of students, enabling experimentation with different forms of dialogic talk and identities. Shifts in discourse, confidence and identity positioning were particularly marked in "lower-attaining" students of lower socio-economic status. Teachers' metadiscoursal reflection resulted in changes in teacher-student relationships and classroom talk characterised by tentativeness, permitting knowledge to be contested.