The purpose of this study was to examine the progression in students\' understanding of the
concept of chemical reaction according to their learning experience. The 235 students were
selected from a middle school (8th and 9th), two high schools (10th and 12th), and a university
(1st and 4th). The data were collected through an open-ended written test and interviews. The
open-ended written test was administrated to all students and some representative students
were interviewed. The interviews were semi-structured and the questions were based on the
written test items. The data were used to identify the characteristics of progression in
understanding of chemical reaction and the differences in students\' understanding. The results
showed that students, who had little understanding of key aspects needed to understand
chemical reaction, had difficulties in understanding of chemical reaction. There were few
students who had a deep understanding of key aspects to make up a satisfactory explanation
of chemical reaction, although university students have learned all aspects of chemical reaction.