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Hand preference, speed of movement of each hand and vocabulary were examined in a random sample of children aged 3 1/2–15 years. The distributions of preference and relative manual speed were found unchanged during growth. Sex differences in preference and skill indicated that females are more asymmetrical to the right than males. Right-, mixed and left-handers were found in binomial proportions in both sexes. A linear relation between degrees of preference and degrees of relative manual skill was demonstrated. The vocabulary distributions of right-, mixed and left-handers differed; that of consistent left-handers was displaced upwards, that of mixed handers spread out to give a significant excess of mixed handers among those of lower IQ. The implications of these findings for the basis of lateral asymmetry and for the relations between laterality and language development are considered. Norms for speed of movement in each hand are given which can be used to assess manual disability.