ABSTRACT This study aimed to investigate the development of computational modelling performances of students during the computer-assisted system (CAS) integrated ACODESA method based on Habermas’ construct of rationality. The participants included 22 university students. In the study, in which the embedded design was utilised, the qualitative phase aimed to examine the computational modelling performances of the students during the stages of CAS integrated ACODESA method. It was determined that the students showed improvement in modelling the Riemann sum accurately with CAS, and in choosing to use for loop to determine the area of the rectangles that represented the Riemann sum, and in comprehensibility and acceptability. In the quantitative phase of the study, pre and post-tests were conducted to determine the effect of the CAS-integrated ACODESA method on computational modelling performances of the students. The computational modelling scores were compared with the paired samples t-test. It was found that CAS-integrated ACODESA method made statistically significant effect on computational modelling performances of the students.