This paper reviews studies in which scores on Piagetian tests of logical thought were correlated with IQ, mental age (MA) and chronological age (CA), and examines the possible effects of the size of the age range and mean age of subjects on these correlations. The data included 44 groups of subjects obtained from 36 studies in which Piagetian and intelligence tests were administered to intellectually normal children (mean IQ=109) from the preoperational through formal operational periods (40 to 216 months of age). Results revealed that averaged correlations between Piagetian tests and MA were consistently higher than the corresponding correlations for IQ and CA. The mean age of the subjects and no effect on the size of correlations between Piagetian tests and IQ, MA and CA, but the size of the age range was found to significantly affect the IQ and CA correlations (Piagetian tests/IQ correlations were higher within a narrow age range; Piagetian tests/CA correlations were higher within a wide age range; Piagetian tests/MA correlations showed no effect for size of age range). It was concluded that MA scores yield higher and more consistent correlations with Piagetian tests than either IQ or CA scores, and are not affected by the age range or mean age of the subjects sampled. (Authors/ED)