A key obstacle to measurement is the aggregation problem. Where indicators tap into common latent traits in theoretically meaningful ways, the problem may be solved by applying a data-informed ("inductive") measurement model, for example, factor analysis, structural equation models, or item response theory. Where they do not, researchers…

Examines the issue of object sorting in early infancy. Forty-eight infants at 6, 9, and 12 months were presented with eight sets of small, manipulable objects. At six months, selective manipulation was absent; at nine months, 94 percent of the infants sequentially touched similar objects and at 12 months 100 percent did so. (Author/DB)

Examined developmental changes in the use of distance-based and calendar-based approaches to estimate the recency of two events. Found that children's ability to discriminate temporal relationships between two events appears by four to five years of age. In contrast, use of calendar information and cognizance of annual patterns was found only in…

Reviews evidence against theories about preschool childrens' egocentricity and cognitive ineptness in the areas of classification, communication, number and order concepts, memory skills, and capacity for reasoning about causal relationships. Holds that preschoolers have been misunderstood because researchers tend to approach them with tasks…

Demonstrated is a covariance principle that causes the observer to assume that if one aspect of a two-dimensional figure (its perimeter or its area) is conserved, the other aspect must also be conserved (pseudo-conservation). Mentally retarded individuals, assuming no such fixed relationship, correctly judged the changed state of the nonconserved…

Six mildly and moderately retarded children (ages 6-8) were instructed in the Piagetian constructs of unidimensional classification and/or seriation using the "Piacelleration" learning set technique. After one semester, subjects made significant gains on: classification and seriation tasks, the Peabody Picture Vocabulary Test, and the…

Describes longitudinal study of the development of understanding of two logical properties of number by 36 children during the first three years of primary school in Glasgow. Piagetian tests and number skills tests were administered to explore the acquisition of number as class and number as order concepts. (Author/LRW)

Through seriation, verbal seriation, and conservation tasks, investigated blind, partially sighted, and sighted children's understanding of quantity. Subjects were 81 children equally dispersed through these 3 groups. Age range was 4 to 17 years. Found similarity in concept acquisition among three groups that extended beyond quantity conservation…