This study examined changes in the effect of socioeconomic status (SES) on reading achievement at individual and school levels between 1991 and 2001. Data from 9 countries that participated in both the International Association for the Evaluation of Educational Achievement (IEA) Reading Literacy Study 1991 and the Trend Study in the Progress in International Reading Literacy Study (PIRLS) 2001 were included in the analyses. The hypotheses of increased between-school differences of reading achievement and a higher SES effect on reading were tested by applying a 2-level 2-group structural equation modelling technique and a factor score approach. The hypotheses were partially confirmed by the empirical evidence from Greece, Singapore, and the USA. The explanations of these results may be the insufficient data and low statistic power. A refined hypothesis may be needed for further investigation. (Contains 8 tables and 1 figure.)