Most European secondary-school systems are articulated by different forms of an academic-vocational divide that are critical in understanding the (re)production of social inequality. By providing distinct curricular and pedagogical codes and a markedly different distribution of knowledge between tracks, tracking leads to profound and distinct learning opportunities for students. The objective of this article is twofold: first, we wish to enquire into the relationship between tracking and knowledge distribution as explained and represented by teachers; second, we aim to identify the mechanisms explaining this relationship as acknowledged in these actors' discourses and experiences. The analysis draws on 72 in-depth interviews with principals, coordination teams and tutors from lower-secondary education, the Baccalaureate and VET in eight schools in Barcelona. The results provide, on the one hand, a thick description of the dichotomised attributes that teachers assign to academic and vocational knowledge. On the other, we identify three principal mechanisms that, according to the school actors who were interviewed, explain the segmented distribution of knowledge between the Baccalaureate and VET: the stratification of the school system, the grammar of secondary schooling and the learning cultures of both tracks.