Behavior Genetics, Vol. 33, No. 3, May 2003 (© 2003) Phenotypic and Behavioral Genetic Covariation Between Elemental Cognitive Components and Scholastic Measures Dasen Luo, 1,3 Lee Anne Thompson, 2 and Douglas K. Detterman 2 Received 25 July 1999 — Final 5 Nov. 2002 The study subjected nine elementary cognitive task variables from the Cognitive Assessment Tasks (CAT) and three scholastic measures from the Metropolitan Achievement Test (MAT) to phenotypic and behavioral genetic structural equation modeling based on data for 277 pairs of same sex monozygotic (MZ) and dizygotic (DZ) twins from the Western Reserve Twin Project. Phenotypic and behavioral genetic covariation between certain elemental cognitive components and scholastic performance was examined to determine (a) whether these elemental cognitive components contribute substantially to the variance of scholastic performance; (b) whether such contributions vary across different domains of school knowledge or from specific domains to a general aptitude; (c) the behavioral genetic composition of the elemental cognitive components and the scholastic variables; and (d) how the association between the cognitive components and scholastic performance is genetically and environmentally mediated. The results of the study showed that as much as 30% of the phenotypic variance of scholastic performance was accounted for by the CAT general factor, which was presumably related to mental speed. A mainly genetic covariation was found between the mental speed component and scholastic performance, al- though each of the two variables was strongly influenced by both heritability and common fam- ily environment. The magnitude and etiology of the covariation were largely invariant whether mental speed was related to a common scholastic aptitude or to individual achievement mea- sures covering different knowledge domains. Taken in conjunction with previous findings that mental speed has a substantial genetic correlation with psychometric g, and psychometric g has a mostly genetic covariation with scholastic achievement, the findings of the present study seems to point to a more global picture; namely, there is a causal sequence that starts from mental speed as the explanatory factor for both psychometric g and scholastic performance, and the etiology of the causal link is chiefly genetic. KEY WORDS: Behavioral genetic mediation; twins; scholastic performance; elementary cognitive tasks; mental speed; structural equation modeling; intelligence. 221 0001-8244/03/0500-0221/0 © 2003 Plenum Publishing Corporation 1 Indiana University of Pennsylvania. 2 Case Western Reserve University. 3 To whom correspondence should be addressed at Department of Psychology, Indiana University of Pennsylvania, Indiana, Penn- sylvania 15705. Tel: (724) 357-4518. Fax: (724) 357-2214. e-mail: dluo@grove.iup.edu his tasks of basic psychological functions, e.g., reac- tion time, sensory discrimination, etc., and the acade- mic performance of Columbia University students, and such disappointingly low correlations discouraged fur- ther efforts in the following decades to decompose global intellectual abilities into elemental cognitive functions. The endeavor of reducing intellectual abili- ties into elemental cognitive processes was thereafter commonly considered as futile, and attention was mostly directed toward the measurement and classifi- cation of more complex psychometric traits. The con- sequence of focusing on global, complex ability traits INTRODUCTION Nearly a century ago, J. M. Cattell made a widely known attempt to relate basic psychological functions to scholastic performance. His attempt, however, was undermined by near zero observed correlations between