Cross-age studies have suggested that although children's notions of scientific phenomena change moderately with increasing age, certain misconceptions persist from preschool to a higher educational level. The purpose of this study was to diagnose the prevalence of selected misconceptions about the particulate nature of matter among preservice primary school teachers and to compare the findings with the results of lower-secondary learners. The participants in the study were 197 pre-service primary school teachers and 170 ninth graders. The multiple-choice diagnostic test was developed to collect data. In the analysis of the test results, the paired difference test and Pearson's chi-square independence test for the contingency table were used. Frequency analysis was performed for individual questions in the test and percentages were calculated. The results obtained with primary school teacher trainees demonstrate the existence of a number of misconceptions similar to those observed with ninth graders; some misconceptions were observed to even be present significantly more frequently among pre-service primary school teachers. This study confirmed that age maturity and mere knowledge of scientific concepts such as atoms, molecules, etc. do not have to be sufficient to allow students to better understand the particulate nature of matter.