Abstract According to the Luria-Das information-processing theory, impaired planning ability is the source of more generalized cognitive deficits in mentally retarded populations. Also, the model suggests the possibility of relative independence between unit 2 (planning) and unit 3 (coding) abilities for mentally retarded individuals. Consequently, it was predicted that 26 educable mentally retarded (EMR) children would score significantly less well on relatively pure measures of planning ability than 13 younger average-ability children after the children were matched on cognitive processing ability (Mental Age of the Kaufman Assessment Battery for Children). Moreover, it was predicted that teaching an optimal planning strategy to randomly selected individuals of both groups would improve the EMR group's scores relative to the average-ability group. Neither prediction was supported. The results are not inconsistent with the model, but can be explained parsimoniously by neurodevelopmental stage theories also.