How to distinguish normal from disordered children with poor language or motor skills

We tested the Diagnostic and Statistical Manual of Mental Disorders (DSM) hypothesis that so-called specific developmental disorders are marked by a pattern of specific discrepant achievement, and an alternative hypothesis that children with these disorders show a pattern of relatively pervasive low achievement.

Children with a diagnosis of Mixed Receptive Expressive Language Disorder (RELD; n = 21) were compared with children with no previously suspected disorder but low standard language scores ( < 80; n = 22) selected from a representative sample, and children with Developmental Coordination Disorder (DCD; n = 20) were compared with children with no previously suspected disorder but low standard motor skills scores (n = 28) selected from a representative sample.

Children with diagnosed disorders were more pervasive underachievers. The RELD group obtained lower scores on measures of verbal comprehension, emotion understanding, theory of mind, working memory and response inhibition; the DCD group obtained lower scores on measures of perceptual organization, verbal comprehension, receptive and expressive language, and visual inspection time.

We conclude that relatively pervasive underachievement distinguishes disordered from normal low achievers.