Learning natural sciences is not an easy task for students. However children already encounter some or all of the natural sciences from primary school age, and the correct development of natural science concepts should be our goal from an early age. Children learn quickly, gain experience, and thus acquire new knowledge throughout their lives. But won't this knowledge lead children astray? The formation of misconceptions is a common phenomenon, and processes aimed at diagnosing them should be an integral part of classroom teaching practice. Within the framework of assessment for learning, the teacher has at his or her disposal a myriad of formative assessment strategies that provide the teacher with immediate results in terms of student knowledge. However, they do not allow for a deep analysis of the knowledge structure.

The word association method is suitable for mapping the conceptual system and its changes in the context of classroom education. It can be used to investigate the relationship between concepts of individual students or groups of students on a specific topic. This can provide a picture of the structure of students' knowledge. Word association can be used to find out which words the student knows or has in mind. The associative meaning of concepts is appropriate to get a current picture of the structure of learners' knowledge. It may also be worthwhile to examine the associations that students have with a given topic before and after the acquisition of a particular lesson.

Our study focuses on the examination of the concepts related to substances. We use a word association method to investigate the knowledge structure of fourth-grade primary school students about substances.

Acknowledgements:
This paper includes research results gained as a part of the project KEGA no. 001UPJŠ-4/2023 „Implementation of formative assessment in primary school teaching with the focus on the digital form“.

Keywords: Free word association, concepts, primary school students, misconception.