We tested whether developmental coordination disorder (DCD) and mixed receptive expressive language disorder (RELD) are valid diagnoses by assessing whether they are separated from each other, from other childhood disorders, and from normality by natural boundaries termed zones of rarity. Standardized measures of intelligence, language, motor…

Recent developments in the definitional literature on mental retardation emphasize the need to ground the concept of adaptive behavior in an expanded model of intelligence, which includes practical and social intelligence. Development of a direct measure of practical intelligence might increase the likelihood that an assessment of this domain…