Background: Students with intellectual disabilities (IDs) have various learning difficulties and are at risk for school failure. Large inter-individual differences are described for reading, but it is unclear how these vary as a function of grade. The aim of this study was to examine various reading fluency, accuracy and comprehension parameters in second-to-eighth-grade Italian children with either borderline intellectual functioning (BIF) or mild ID (MID). Methods: We examined 106 children with BIF (67 M and 39 F) and 168 children with MID (107 M and 61 F). The children were in the second to eighth grade and were comparable for chronological age (7 to 14 years). They were administered a battery of tests that assessed fluency and accuracy of word, pseudo-word and text reading, as well as text comprehension. Standardised scores allowed us to compare the performance of the two groups with normative values. Results: Children with ID obtained generally low scores compared with normative values. Those with MID had greater difficulty than those with BIF. Furthermore, difficulty was greater for speed than for accuracy measures and for words than for pseudo-words. Difficulty (particularly in the case of reading speed) tended to be pronounced at later grades. Marked individual differences were present independently of MID-BIF subgrouping, as well as stimulus category and reading parameter. Conclusions: As a group, children with ID showed difficulty in reading acquisition; the effect was greater for children with more severe ID, but large individual differences were observed in children with both BIF and MID. Relatively spared pseudo-word reading skills indicate efficient use of the grapheme-to-phoneme conversion routine. This processing mode may prove more ineffective at higher levels of schooling when even in regular orthographies such as Italian typically developing children rely on lexical activation.