To  compare both the reading ability and academic achievement among Farsi speaking mono-lingual fifth graders and their bilingual Aazari and Kordi counterparts, three samples of 153, 132, and 145 (total 430) such students from three cities of Tehran, Maraagheh, and Mahaabaad were selected and then tested. The measures used were the Cloze test of reading ability and a teacher-made achievement test. The analysis of the data revealed a significant difference between the mono-lingual and bilingual groups in both reading ability and achievement. There was no significant difference between the two bilingual groups who scored lower than the Farsi speaking monolinguals, indicating that the texts used nationally are not suitable for all students, especially those whose home language is not Farsi.