Visual, linguistic, reading, and spelling tests were administered to the same 45 children at the end of kindergarten and of first grade. Normal variation, i.e., diversity not related to pathology, was found in the visual and linguistic skills and was shown to be related to reading and spelling achievement for a sample of suburban children of similar socioeconomic status. Individual differences in three visual skills—selective attention to letter information (RT), memory for a component letter (accuracy), and memory for a whole word (accuracy)—and two linguistic skills—phonemic analysis and vocabulary understanding—were reliable over the first year of formal reading instruction and had concurrent validity in that they were correlated with achievement in word decoding/encoding at the end of kindergarten and of first grade. Of these five skills, phonemic analysis accounted for more variance in achievement (52% to 64%, depending upon achievement measure) than any other single skill. Significantly mote variance in achievement was accounted for when both a visual skill (memory for a sequence) and a linguistic skill (phonemic analysis) were considered than when either alone was at end of first grade. The predictive validity of quantitatively defined “disabilities” (at or more than a standard deviation below the mean) was investigated; disabilities in both visual and linguistic skills at the end of kindergarten were associated with low achievement in word decoding/encoding at the end of first grade. Two pairs of identical twin girls (each co-twin taught by a different teacher) were not mote congruent on several achievement measures than two pairs of unrelated girls, taught by the same teacher and matched to each other and a twin pair on verbal ability and age. Normal variation in acquisition of word decoding/encoding probably results from an interaction between genetic individual differences in cognitive skills and the processes of assimilation and accommodation during environmental transactions proposed by Piaget.
Sex-specific quantitative trait loci contribute to normal variation in bone structure at the proximal femur in men
