Didactical analysis of a lesson on proportionality of a primary school textbook using tools of the onto-semiotic approach

Abstract The textbook is a widely used resource in the practice of teaching and, consequently, is a subject of educational research considered from various theoretical perspectives. In this paper, we apply the theoretical tools from the onto-semiotic approach to mathematical knowledge and instruction to perform the didactical analysis of a lesson on proportionality for elementary school (sixth grade; 11-12 years old). The selected lesson allows us to reflect on the instructional process planned by the textbook authors as a means to achieve the students’ learning. The following questions guide the textbook analysis: 1) What is the degree of didactical suitability of the planned instructional process? 2) How should we manage the use of the textbook to increase the process suitability? The method of analysis implemented allows us to obtain the didactic-mathematical knowledge that may help the teacher in making decisions about the textbook possibilities and limitations, when assuming the sociocultural postulates for mathematical learning.