This study investigated the linguistic components of Piaget's class-inclusion task. First, hierarchical classification is examined from both Piagetian and linguistic theory points of view. Then, two general characteristics of child thinking that relate to the different interpretations of the responses to classification questions are discussed: (1)…

A 1-year lag was found between the effect of an intervention intended to promote formal operational thinking in students initially 11 or 12 years of age and the appearance of substantial science achievement in the experimental groups. A one-year lag on cognitive development and an age/gender interaction were also reported. (Author/KR)