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…

A study was designed to develop an instrument and methodological procedure to assess transitive relations within seriation problems in elementary school children using three criteria: explanations, judgments, and strategies. A secondary analysis to assess transitivity used the three criteria according to whether the children were conservers, in…

This study examined the effect of an innovative teaching activity to improve concrete operational thinking skills with preschoolers in Head Start programs. A "learning set" of classification games and seriation games was used to teach the oddity principle and insertion into a series. These games were played with the children using toy ponies and…