Performance of young nonretarded children and children with Down syndrome on Piagetian infant search tasks.

Two groups of 3- to 5-year-old children, a nonretarded and a Down syndrome group, were tested six times over 2.5 months on three Piagetian infant search tasks. Two opposing trends in performance over sessions were evident: Scores of children in the Down syndrome group increased significantly whereas the performance of nonretarded subjects declined. The data suggest that cognitive ability of children with Down syndrome may be poorly measured by single-session testing; also, that in the absence of normative data from nonretarded children, caution is necessary in evaluating the performance of children with mental retardation on tests designed for and validated on younger, nonretarded subjects.