Does age moderate the effect of IQ on the differentiation of cognitive abilities during childhood?

Data from the national standardization of the French version of the WISC-III were analyzed to determine when during childhood the IQ-related process of differentiation appears and how the strength of the relationships among subtests evolves with age in low- and high-IQ groups. Indeed, some recent studies suggest that age might moderate the effect of IQ on the differentiation of cognitive abilities. The whole sample (N = 1, 120) was divided into six groups based on age (7-9, 10-12 and 13-15 yr) and on the mean of the subject's standard scores for Vocabulary and Block Design (mean < 10 vs. mean ≥ 10). Correlations between the remaining eleven subtests were then calculated for each group. Results showed an age-related increase in relationships among subtests for low-IQ participants, but good stability for high-IQ participants. This confirms the hypothesis of an Age × IQ interaction on the degree of differentiation of abilities and suggests that persons with low IQ do not exhibit a less differentiated pattern of intellectual abilities from the outset of their development. Rather, this characteristic seems to appear in late childhood.