Abilities underlying decoding differences in children with intellectual disability

Researchers in recent years have made much progress towards understanding w hy some children struggle to learn to read. However, little of this researc h has involved children with intellectual disability associated with an IQ < 70 (ID, also called mental retardation). In the present analysis, the aut hors examined cognitive similarities and differences between stronger and w eaker decoders, all of whom have ID. The 65 children with ID in the present analysis were initially referred by their teachers for a study that involv ed training basic phonological reading skills. The present analysis compare s 21 children who were excluded from the training study because their decod ing skills were already too high with 44 children whose decoding skills wer e low enough for the training study. The groups were compared on general in telligence, language ability, phonemic awareness and phonological memory. I nitial analyses showed that the stronger decoders were significantly better than weaker decoders in language ability, phonemic awareness and rehearsal in phonological memory, but not in intelligence. They were also significan tly older than weaker decoders. When age was covaried out, the groups diffe red significantly only in rehearsal in phonological memory, although the di fference for phonemic awareness was marginally significant when the poorest performers were excluded. When intelligence is substantially limited, the ability to rehearse or refresh phonological codes in working memory plays a major role in determining children's success in learning to read. This abi lity appears to be more important than intelligence, language ability and p honemic awareness. It is possible that the reason the phonemic awareness me asure was not as good at distinguishing the groups as the phonological rehe arsal measure was because the former did not involve assembling phonologica l output. It is suggested that it is the combination of poor phonological r epresentation and poor phonological output assembly that makes decoding dif ficult for some children with ID.