Equity in educational outcomes, particularly reading, is an important policy issue in all countries. This research used data from PIRLS 2006 participants, including 15 EERA member countries, to explore an approach to measuring equity in reading achievement internationally at the fourth grade. Berne and Stiefel’s (1984) concept of horizontal equity was employed as a guiding framework. Relative risk ratios were selected as a measurement approach and a composite measure, the Relative Risk-Percentage (RRP) Equity Index, was created 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. Overall, having parents with less than secondary education and not speaking the language of instruction before starting school were associated with inequity in reading achievement in the largest number of PIRLS countries.