Study of the similar structure hypothesis with mentally retarded adults and nonretarded children of comparable mental age.

The similar structure hypothesis was tested by comparing the performance of mentally retarded adults and their nonretarded mental age peers on a series of Piagetian tasks. We controlled for variables that influence the testing of mentally retarded subjects and performance on Piagetian tasks. Statistical analysis revealed that five tests favored the developmental position whereas two tests favored the difference position. Qualitative analysis provided reason to question the validity of two of the seven tests. Nevertheless, the evidence still favored the developmental position 4:1. Corollaries challenged the use of vocabulary tests for matching and raised a caveat concerning the acquisition by mentally retarded adults of key concrete operations skills.