Engaging with learner errors in mathematics classrooms is an important aspect of teacher pedagogy which can support learner identification with mathematics. This study examined the opportunities that teachers provided for the construction of learner identities based on how the teachers spoke about and interacted with learner errors in two secondary school mathematics classrooms. Data were collected over two years in the form of videotaped lessons, field notes, photographed learner notebooks and audiotaped interviews with participants, and were analyzed qualitatively. Two ways in which teachers spoke about errors are discussed: errors are contagious and errors are lessons. How the teachers spoke about and interacted with errors were informed by their views of learners and their reasoning in mathematics, which shaped the identities they offered learners. We show that while learners' experiences of their teachers' approaches to errors informed their identification with mathematics to some extent, the learners also played a role in the construction of their mathematical identities.