Developing academic, or school-based, literacy poses a significant challenge for many students, because the language through which academic subjects are presented is markedly different from the social language that students use in everyday ordinary life. This article focuses on one aspect of academic language, the functions of nouns and nominal structures in constructing knowledge in different subject areas and the challenges they present for comprehension of academic texts. Using a functional linguistics framework and analyzing written texts from language arts, science, and history, at elementary and secondary levels, we illustrate the ways nominal expressions expand the amount of information in a clause, establish and maintain reference, and enable information to be distilled and further expanded. We also show how the semantic features of the nominal elements vary in different academic registers, as texts introduce grammatical "participants" of different types according to the purposes of the text. We suggest that the notion of linguistic register offers a means of transcending debates about academic language, enabling a pedagogy that can raise students' consciousness about specific grammatical resources and how those resources function to construct knowledge in the language of schooling.