This article centres on the problem of raising the level of school knowledge, particularly science knowledge, for all. The article describes studies in science education developed in Portugal by Morais and Neves and collaborators. These studies are mainly based on Bernstein's model of pedagogic discourse (PD), and on his theorisation on knowledge structures. The concepts of classification (power) and framing (control) are revisited to highlight their potential to characterise educational code modalities, through an extensive external language of description. Examples of instruments are presented in order to discuss the potential of using classification to analyse the status and the conceptual level of school knowledge (the what of PD) and also of using classification and framing to distinguish power and control relations between subjects, discourses and spaces (the how of PD), in educational texts/contexts. Educational code modalities which encourage school success are discussed in terms of their implications for greater equity.