Correct understanding of the equals sign is the key to understanding arithme- tic, and a fundamental concept important for learning other areas of mathematics. Research around the world repeatedly mentions problems with correctly understanding the equals sign, emphasising the limited view of the equals sign as a command ”to calculate“ among students. The goal of the research was to identify the development of the concept of equality in line with the operationalised levels (operational, relational, and relational in the context of real-life prob- lem solving) and determine differences in understanding between students of the second (N = 190) and the fourth (N = 210) grade of primary school. The research was carried out using the testing technique. The research results show that students do not possess sufficiently developed relational understanding of the equals sign and that operational understanding prevails. Students of the fourth grade demonstrated better understanding of the equals sign at all levels of under- standing than the second graders.

The paper draws attention to the difficulties associated with the introduction of symbols and symbolic notation in junior grades of primary school. In this context, the paper draws special attention to the proper understanding of the concepts of unknown and variable at this age and also point to a wide range of problems related to understanding letters as symbols used to denote an unknown or variable in early algebra. The shaping of a real-world context problem at different levels of abstraction is exemplified with the formation of the concepts of unknown andvariable. In this process, real-world situations represent a source of developing mathematical concepts, tools and procedures in which students can apply their mathematical knowledge at a later stage because it gradually becomes more general and formalized and therefore less contextrelated.