This paper reports findings from 111 Ss tested with the Stanford-Binet (S-B) at preschool and adolescence who were administered the S-B and WAIS at adulthood. Correlations of preschool IQs with adult S-B and full WAIS IQs are .59 and .64; of adolescent IQs with adult IQs, .85 and .80. Mean S-B IQ increase from adolescence to adulthood is 11 points, indicating that mental growth continues beyond 16 years. Males show more IQ gain after adolescence than do females (p < .01). Girls with high IQs increase least. Analysis of increases in percent passing S-B items shows more growth after adolescence in abstract reasoning and vocabulary than in rote memory and practical reasoning. Preschool verbal and memory items are better predictors than nonverbal items of both verbal and performance adult IQs. Pattern of individual differences in relative amounts of these abilities shows some stability over 25 years.

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Ai assumption is implicit in much of the work of clinicians who diagnose mental deficiency that the behavior of mentally deficient subjects is different qualitatively from that of normal subjects of like mental age. Ordinarily this assumption rests upon the informal observation that certain items on standardized scales of intelligence are either less difficult or more difficult for defectives than for normal subjects of equal mental level. The defective is generally considered to be superior in items depending upon rote memory, for example, or in items such as vocabulary or absurdities which might depend upon past experience and therefore upon chronological age.The validity of this assumption has ordinarily been examined through analyses of responses of normal and deficient subjects to standard test items. Numerous studies employing the 1916 Stanford-Binet Scale in this way have established the fact that certain items on the scale are either more or less difficult for defectives than for normals. The usual explanation of these differences has been in terms of the wider experience of the older defectives, al-* The authors wish to express their appreciation to Mrs. V. J. H.

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