Researchers in the field of science education believe that people's attitudes about learning will have a significant impact on their future learning and what they learn from science will not be irrelevant to their views and attitudes. Accordingly, most questionnaires have been developed to measure attitudes towards science. One of the newest questionnaires is the Colorado Learning Attitudes about science, known as CLASS. This questionnaire has not been standardised in Iran for the use of researchers in the field of education and psychology. The current descriptive research has been based on instrument designs and examined their psychometric properties. In this study, 476 high school students in science and mathematics courses were recruited to evaluate the psychometric properties of the questionnaire. Confirmatory factor analysis was used to investigate the questionnaire structures and a graded response model in Polytomous Item Response Theory (IRT) was used to analyse items. The Cronbach’s alpha for all eight factors of the questionnaire ranged from 0.701 to 0.891. All the eight factors perfectly fitted into the Polytomous IRT models, in addition to having diagnosis and threshold parameters. In terms of classical measurement, indicators such as reliability and validity of the structure as well as the estimated parameters in the Polytomous IRT model, the items and structure of this questionnaire could be considered as desirable. Therefore, the authours would recommend using the Persian version of this questionnaire to examine attitudes about science, especially physics, appropriately.
