What is the relationship between our mental activity and the empirical objects of the world? Kant raised this question in the Critique of Pure Reason and attempted to answer it by arguing that between the realm of concepts and that of sensuous phenomena lies the schema. Piaget re-elaborated the Kantian concept of schema and since then it has been extensively used in constructivist and psychological accounts of the mind. In this article, I discuss Kant's and Piaget's concept of schema from a semiotic-cultural perspective. Attention is paid to the epistemological premises on which the Kantian and Piagetian theoretical elaborations of the concept of schema were based and the role that signs played therein. I contend that the schema and its genesis can be better conceptualized if we take into account linguistic and non-linguistic mediated actions embedded in the social processes of meaning production and knowledge objectification. My discussion interweaves epistemological concerns with the semiotic analysis of a group of Grade 11 students dealing with the mathematical understanding and description of a natural phenomenon — the movement of a body along a ramp in a technological environment.