The aim of this paper is to propose the validity of functional approaches within discourse analysis as a tool for selecting classroom material. By taking into account the linguistic realization of the three main contextual variables, namely field, tenor, and mode, and their impact on the function of language within each particular context of communication, we believe that the task of selecting and devising materials for CLIL setting shall be eased. This hypothesis becomes the point of departure for this article, where we present an analysis of six texts used for teaching Science using L2 English as the means of instruction. Conclusions are obtained about the importance of considering that any type of language used in a text has a function w...