Description:
This study aims to investigate Iranian students’ understanding of the particulate nature of matter via a cross-age study. The students involved in this study were high-school students who studied chemistry at the basic level (9th grade) and advanced level (10-11th grade), totaling about 160 individuals. In the study, a test comprising six open-ended and multiple choice diagnostic questions, students' drawings, and semi-structured interviews were employed to collect data. According to the The findings showed that students have many various and different conceptions about matter and many of which have not been previously documented. Further, it was concluded that there is no clear link between students’ conceptions and their grades. In the light of the study, it can be suggested that due to the Ministry of National Education’s recent revisions of the science education curricula and instructional materials, further emphasis should be given to the particulate nature of matter and its modeling in relation to the ed course books.