Reading literacy of immigrant students has often been a matter of investigation. Still very little is known about the effects of immigrant student ratio at the class level on student achievement. This gap can be filled by analyzing PIRLS data. Beyond achievement data, PIRLS provides a wide variety of background information including student’s immigration history. Unlike PISA, PIRLS collected information from intact classes, thus class-level analysis can be performed. This study examines (a) the amount of students attending classes with high proportions of immigrant students (b) the effects of classroom composition on native and immigrant student’s reading literacy, and (c) whether migration-based classroom composition has still an effect on reading literacy when controlling for socioeconomic background indicators. Analyses are made for the 16 PIRLS 2006 countries in South-East Asia, Western Europe and North America exceeding 10 % immigrant students at 4th grade. Results of this study provide valuable information for policy makers and practitioners on how to integrate immigrant students into classes.