The relationship between consistency of hand preference, left hemispheric specialization, and cognitive functioning was examined in an ongoing longitudinal investigation. Children were classified as consistent or inconsistent in their hand preference across 5 assessments from ages 18 to 42 months. Findings demonstrated that (a) this early classification continued to reveal differences in cognitive functioning from 10 to 17 years but only for girls, (b) consistent girls' performances were continually higher relative to the inconsistent girls on measures of verbal intelligence and reading achievement, (c) differences between the female groups were specifically related to left-hemispheric language specialization, and (d) one factor influencing the consistent girls' development may be the amount of reading exposure received during infancy.