In the present paper the results of the research on the theoretical levels of teaching content given in textbooks are summarized. The theoretical levels obtained from the analysis of the teaching material with respect to the actual state of scientific knowledge have been investigated from the point of view of their applicability in the teaching material as a whole as well as of the usefulness of textbooks for students as far as their learning from textbooks is concerned. The results of the research show that the high interpretation levels of teaching content have been the cause of a bad comprehensibility of textbooks which results in a low attractivity not only of themselves, but also of the teaching objects as such.