This paper aims to show how ethnography is used to explore the pedagogical practice in teacher education, how it is structured, transmitted and acquired. It has two foci, which gives the paper a dual purpose: to identify and describe (even theoretically) a key substantive issue and to reflect on the use of ethnography in this. The empirical material is drawn from an ethnographic study where a group of students were followed 20 weeks during a mathematic course. The material discussed here, represents 20 hours of participants observations from lectures in mathematics, and 8 conversional interviews with students. The paper uses Bernstein’s concepts of code and the modalities of pedagogic transmission and acquisition, and his typology of vertical and horizontal discourse, to show how a strong classified and framed practice block student teachers from developing vertical knowledge structure in mathematics. The mathematic knowledge that students are subjected to takes more the form of a horizontal discourse and that is problematic for their professional development in that a horizontal discourses reduce student access to important forms of knowledge by which they can challenge tradition and consciously change their practice (Bernstein, 2000, 2003).