Handedness, clumsiness and cognitive ability.

An unselected group of 170 children aged between eight and nine years was given tests of intelligence, reading ability and manual dexterity. A 'target' group of children was selected on the basis of very poor performance with the non-preferred hand. Using an extension of Satz's pathological left-handedness model, it is argued that there should be a higher proportion of left-handers in the target group than in the remainder of the sample: this prediction was confirmed. It was also predicted that the target group should have a higher incidence of neurological disorder, and that left-handers in the target group should have a lower incidence of familial sinistrality than other left-handers. Partial confirmation of these predictions was obtained. The target group was impaired on cognitive tasks. It is argued that skill with the non-preferred hand may be more meaningful than direction of hand preference as a basis for understanding relationships between handedness and ability.