The aim of this study was to investigate the types of errors produced by three participant groups (individuals with Down syndrome, with moderate learning disability, and typically developing children) whilst completing the Raven's Coloured Progressive Matrices task. An analysis of error categories revealed that individuals with Down syndrome produced a significantly different pattern of errors to the comparison groups. This difference remained, though was less marked, when the groups were matched on overall task performance. Consequently, even when the groups were making the same "number" of errors, they were not making the same "type" of errors. An investigation of age-related error patterns revealed that there was a significant change in the types of errors made by typically developing individuals with age. However, no significant age-related change was found in the types of errors made by participants with Down syndrome. The analysis also provided evidence that individuals with Down syndrome were not producing error types appropriate for their chronological age, or for their overall level of task performance. Possible explanations for these differences in terms of problems of integration of perceptual information, reduced visual acuity, and a lax criterion for task completion in Down syndrome are considered.