The purpose of this study was to determine the state of secondary school students? cognitive structures about argument and related concepts and to reveal the change in their cognitive structures regarding these concepts after the implementation of the argumentation-oriented approach in science lessons. This study was conducted in Grade 6, 7, 8 classes, including a total of 80 students. This study follows a pre-experimental one group pretest-posttest design. Students were administered a word association test (WAT) covering argument and related concepts prior to and following the lessons. The results obtained from the WAT show that the students? cognitive structures progressed from the pretest to posttest, with an increase in the number of response words and connections between words, and with a change in the nature of these connections. As a result of teaching science lessons through argumentation, it was detected that cognitive structures of students regarding argument and related concepts indicated changes in the right way