Submicroscopic representations are important at all educational levels for establishing the students’ understanding of chemical concepts at the particulate level. The research aim was to establish the understanding of the states of water and of the process of water freezing at the submicroscopic level across the education vertical. The quantitative research sample was composed of 31 seventh graders of elementary school, 29 students of the first year of gymnasium and 20 students of the Chemistry Study Course at the Faculty of Education of the University of Ljubljana. The measurement instrument of the research was a knowledge test with four authentic problem tasks, which included animations of particle movements. The knowledge test was displayed on the computer screen as screen images. In individual task solving, eye movements were monitored by an eye tracker, and the responses were simultaneously recorded.
The research results show the increase in successful noting of the correct justifications for the choice of a submicroscopic representation across the education vertical only in the case of a solid state of water (primary students 9,7 %, secondary students 13,8 %, and faculty students 55,0 %). The frequency of incorrect understanding of the movement of water particles in the solid state decreased across the education vertical (primary students 51,5 %, secondary students 41,4 %, and faculty students 15,0 %). The misunderstanding of the motion of particles in the liquid (primary students 25,9 %; secondary students 30,9 %) and in the gaseous state of water was present only in primary students and in secondary students (primary students 6,4 %; secondary students 6,8 %). The misunderstanding of the properties of particle movements in the solid state in the task of water freezing increased across the education vertical (9,6 % of primary students, 10,3 % of secondary students, 15,0 % of faculty students). According to the research results, the understanding of 3-D dynamic submicrorepresentations of states of water and its changes of state should be developed in primary and secondary schools.