This study, conducted in one high-achieving secondary school in a disadvantaged area in the Western Cape province of South Africa, asks whether mathematics teachers alter their "talk" across the face-to-face and computer-based lessons. Data were gathered through video recordings of teacher/student interactions across ten face-to-face and computer-based mathematics lessons conducted by two teachers. Findings indicate that the teachers studied significantly altered their "talk" across the two contexts, with a medium effect size. Further, a significant association at a medium effect level between any two of the three variables--location of lesson, "talk" type and scale of interaction--was found. In particular, teachers used significantly less mathematical talk in the computer lessons. As language is the primary mediator of conceptual acquisition (Vygotsky, 1978), this calls into question what mathematical concepts are learnt in a computer-based lesson.