An investigation of Piaget's theory of object concept development through a series of six tasks administered in a combined longitudinal/cross-sectional design (which incorporated a number of methodological controls). Subjects were 36 infants who received the six tasks during each of three testing sessions over a 6-month period. (Author/ED)

The Perry Preschool Project assessed longitudinal effects of a 2-year program consisting of a daily 3-hour cognitively oriented nursery, a weekly 90-minute home visit, and less frequent group meetings of the pupils' parents. Subjects consisted of 3- and 4-year-old Negro disadvantaged and functionally retarded children, whose pretest scores on the…

In this study an attempt was made to obtain a developmental dimension for estimating longitudinal development on the basis of cross-sectional data. To check the validity of this approach, the cross-sectional data were compared with true longitudinal data. Forty-three public school children were given a series of conservation tasks in four…