Equity in educational outcomes, particularly reading, is an important policy issue in countries around the world. This dissertation used data from PIRLS 2006 to explore an approach to measuring equity in reading achievement internationally at the fourth grade. Relative risk ratios were selected as a measurement approach and were used to create a composite measure, the Relative Risk-Percentage (RRP) Equity Index, to compare equity in reading achievement across countries. This index was used to present the likelihood of scoring below the PIRLS 2006 Low International Benchmark for student groups that were traditionally at risk for low reading achievement compared to other students. The `at risk' student groups that were the focus of this study included those with low parental education, who spoke a language other than the language of instruction, who attended urban or rural schools, and who were boys. To complement the RRP Equity Index results, the relative likelihood of students scoring within the lower 20 percent of their country's reading achievement distribution was also presented. The results of these analyses showed that students with these characteristics were more likely than other fourth grade students to have low reading achievement in a number of the PIRLS 2006 countries. Overall, having parents with less than secondary education and not speaking the language of the test before starting school were associated with inequity in reading achievement in the largest number of PIRLS 2006 countries. As an example of how individual countries could further explore potential reasons for inequities in reading achievement highlighted by the RRP Equity Index, logistic regression models were built for Germany, Iran, and Romania. These models explored the extent to which statistically controlling for differences in resources could diminish the effect of being in an `at risk' group on reading achievement. In all three countries examined, resources explained a substantial proportion of the risk for low reading achievement. Though the logistic regression model results were country-specific, lacking books in the home was strongly associated with lower reading achievement in all three countries.