This study identifies the Argumentative Outlines (AEs) with which the propositional knowledge transmitted in the School Texts (TE) of two subjects of the second basic cycle of education in Chile is justified. Using a top-down approach, a corpus of 26 school texts distributed by the Chilean Ministry of Education between 2012 and 2016 was analysed. The arguments were extracted and then their argumentative schemes were determined, which were characterized by their types of reasoning, their material relations and their rules of logical inference. The results show 1) scarce justification of propositional knowledge transmitted in the TE; 2) justification by means of arguments only of the Reasoning and Application of rules to cases type and 3) scarce justification of propositional knowledge in the Language and Communication subject. The first implies insufficient epistemic conditions of propositional knowledge transmitted in the TE to be acquired by students. The latter implies a high presence of causal-deductive reasoning and a total absence of source-based reasoning. The third implies disciplinary variation in the way knowledge is communicated.