Taking Swedish secondary school students as a point of departure, this article focuses on aspects of teaching and learning critical literacy and specifically on what students identify as argumentative text structure. Challenges connected to teaching critical literacies can be considered quite big, since studies show that students have difficulties in identifying argumentative text structure and that teachers feel insecure about what kind of knowledge is required as well as how to organize teaching of critical literacies. By using Bernstein's notions of horizontal and vertical discourses as well as Gee's notions of primary and secondary Discourses, we describe the interaction between personal, informal discourses and the more formal, academic discourses in the teaching and learning of critical literacies. The empirical material contains observations in two secondary school classrooms as well as written student material from a study focusing reading of argumentative texts. Our result shows that metacognition is a key component of reading instruction that supports the development of secondary Discourse and vertical discourse. Metacognition also facilitates a critical approach to different texts, and is an important aspect of critical literacies perspectives.