This article reviews two aspects of human learning: (1) people draw inferences that appear to rely on hierarchical conceptual representations; (2) some categories are much easier to learn than others given the same number of exemplars, and some categories remain difficult despite extensive training. Both of these results are difficult to reconcile…

In this special section, 6 articles address the provocative question of how to determine the boundary between difference and deficiency, for children who differ from the mainstream in some way--language, hearing, cultural background, socioeconomic status, or social understanding. Our commentary considers these articles in light of current models…

Potential benefits of using item response theory in test construction are evaluated, based on the experience and evidence accumulated during 9 years of using a three-parameter model in the construction of major achievement batteries. Specific benefits covered include obtaining sample-free item calibrations and item-free person measurement,…

Extends dynamic model of cognitive growth proposed by van Geert in three directions: (1) added a term to consider exposure to material to be learned; (2) developed method to apply model to cross-sectional studies; and (3) developed procedure to scale cognitive abilities tests with items of varying difficulty. Tests model with 2- to 15-year-olds'…