We present a year-long case study that documents the interactions between a teacher-research-mentor (TRM) and two 11th grade students working in their school laboratory on an extended inquiry project that is part of reformed mandatory requirements for advanced-level matriculation in physics. Both the students (females) and the TRM (male) are Arab citizens of Israel, and the school is a public Arab school in Israel. Data were collected through videotaped participant observation of authentic working sessions and interviews with the TRM and the students. The analysis combines an ethnographic account with discourse analysis informed by a sociolinguistic approach that aims to answer the following research questions: (1) how are a teacher's identity-narratives reified in teacher-student discourse in authentic sessions of mentoring students' inquiry? (2) how do they shape students' learning? and (3) how do they emerge from social-historical contexts? The findings problematize the challenges involved in engaging students from nondominant communities in science, technology, engineering, and mathematics learning. The analysis articulates the complexity of this challenge by showing how teachers' identity narratives shape the social construction of student-teacher discourse, generate tensions that undermine successful implementations of reformed learning experiences, and how this vicious cycle is profoundly influenced by the embedding social and historical contexts. The implications for research and practice are discussed.