Abstract
We evaluated over 200 participants semiannually from 12 to 48 months of age on measures of intellectual (Bayley Scales, Stanford-Binet Scale) and verbal (MacArthur-Bates Inventory, Peabody Picture Vocabulary Test) status. Structural equation modeling and hierarchical linear (growth curve) analyses were applied to address the nature of development and individual differences during this time. Structural analyses showed a strong and robust simplex model from infancy to the preschool period, with no evidence of qualitative reorganizations or discontinuities. Growth-curve modeling revealed significant associations between level factors across the early and later measures of cognition, providing further evidence of continuity; the growth trajectory from the Bayley through 24 months predicted growth in a nonverbal factor, but not in a verbal factor. Altogether, the findings reveal continuous and stable development in intellectual function from late infancy through the preschool years. Additionally, the high level of continuity demonstrated across these ages was observed to be largely independent of growth in vocabulary.