The purpose of this study was to compare the level of concept attainment achieved by students enrolled in a Physical Science Study Committee (PSSC) physics course with that achieved by students enrolled in a traditional high school physics course. A sample of 265 PSSC students and 219 enrolled in the traditional course participated. The instrument used, constructed by the investigator, was Assessment of Concept Attainment: Refraction, including the Concept Attainment Test (CAT) and the Concept Knowledge Test (CKT). The CKT was used as the control for the concept knowledge factor and the Otis-Lennon Mental Ability Test (OLMAT) for the mental ability factor. Comparison of mean scores showed the PSSC group had acquired a significantly greater amount of knowledge of the concept and the OLMAT indicated similar comparative data. The multiple analysis of covariance procedure used showed no significant difference in level of concept achieved and it was indicated this might be due to initial differences between the groups in the particular factors. The comparison of the regression coefficients showed that the concept knowledge factor was by far the more important determinant of concept attainment as measured by CAT scores. The author suggests that the study contradicts the opinion of those who argue that the traditional science courses are more effective in imparting factual knowledge. (Author/EB)