The Genetic Basis of Academic Achievement on the Queensland Core Skills Test and its Shared Genetic Variance with IQ Mark A. Wainwright, 1,2,3 Margaret J. Wright, 1 Gina M. Geffen, 2 Michelle Luciano, 1 and Nicholas G. Martin 1 Received 21 June 2004—Final 28 Sept. 2004 First, this study examined genetic and environmental sources of variation in performance on a standardised test of academic achievement, the Queensland Core Skills Test (QCST) (Queensland Studies Authority, 2003a). Second, it assessed the genetic correlation among the QCST score and Verbal and Performance IQ measures using the Multidimensional Aptitude Battery (MAB), [Jackson, D. N. (1984) Multidimensional Aptitude Battery manual. Port Huron, MI:Research Psychologist Press, Inc.]. Participants were 256 monozygotic twin pairs and 326 dizygotic twin pairs aged from 15 to 18 years (mean 17 years ± 0.4 [SD]) when achievement tested, and from 15 to 22 years (mean 16 years ± 0.4 [SD]) when IQ tested. Univariate analysis indicated a heritability for the QCST of 0.72. Adjustment to this estimate due to truncate selection (downward adjustment) and positive phenotypic assorta- tive mating (upward adjustment) suggested a heritability of 0.76 The phenotypic (0.81) and genetic (0.91) correlations between the QCST and Verbal IQ (VIQ) were significantly stron- ger than the phenotypic (0.57) and genetic (0.64) correlations between the QCST and Per- formance IQ (PIQ). The findings suggest that individual variation in QCST performance is largely due to genetic factors and that common environmental effects may be substantially accounted for by phenotypic assortative mating. Covariance between academic achievement on the QCST and psychometric IQ (particularly VIQ) is to a large extent due to common genetic influences. KEY WORDS: Academic; achievement; heritability; intelligence; twins. INTRODUCTION There is abundant evidence that academic achieve- ment is correlated with IQ for both school grades and standardised achievement test scores (see review by Jensen, 1998). Despite a large number of studies demonstrating the significant heritability of IQ there has been limited research examining the heritability of academic achievement or the relative genetic and environmental contributions to the correlation between academic outcomes and IQ (see review by Petrill and Wilkerson, 2000). The purpose of this paper is two-fold. First, to investigate the heritability of a standardised test of academic achievement known as the Queensland Core Skills Test (QCST) (Queensland Studies Authority, 2003a), which is sat by approximately 85% of Queensland year 12 (final year of schooling, typically aged 17) students, many of whom progress to tertiary studies; and second, to examine the extent to which shared genetic factors influence covariance between total score on the QCST and psychometric IQ (Verbal and Performance). While previous studies have examined the genetic correla- tions between academic achievement and IQ in 1 Queensland Institute of Medical Research, Brisbane, Australia. 2 Cognitive Psychophysiology Laboratory, School of Psychology, University of Queensland, Brisbane, Australia. 3 To whom correspondence should be addressed at Queensland Institute of Medical Research, Post Office Royal Brisbane Hos- pital, Herston, Brisbane, QLD 4029, Australia. Tel.: +617 3362 0272, Fax: +617 3362 0101, e-mail: markWa@qimr.edu.au 133 0001-8244/05/0300-0133/0 Ó 2005 Springer Science+Business Media, Inc. Behavior Genetics, Vol. 35, No. 2, March 2005 (Ó 2005)