The analyses reported in this paper seek to examine: (1)the factor structures underlying the tests employed in the Reading Comprehension and the Reading Literacy Studies. In particular, it is of interest whether or not the assumption holds of a common factor or trait, that underlies the processes involved in reading comprehension, as argued by Thorndike (1973a). If this were not the case, it would not be appropriate to calculate a total score which is necessary to equate student performance over time. Confirmatory factor analysis (CFA) is used to examine this issue. (2)whether or not similar results are obtained across countries from an examination of the different factor structures. This is of importance in order to examine whether or not the reading comprehension of different languages in which the tests were administered would follow similar structures.