Research on the genetic influences on different abstract reasoning skills (fluid intelligence) and their interrelation (especially in childhood/adolescence) has been sparse. A novel cognitive test battery, the Verbal and Spatial Reasoning test for Children (VESPARCH 1), consisting of four matched (in terms of test-procedure and design) subtests assessing verbal [analogical (VA) and categorical (VC)] and spatial [analogical (SA) and categorical (SC)] reasoning, was administered to a population based sample of 12-year old twins (169 pairs). Multivariate analysis was conducted to explore the genetic relationship between the four cognitive sub-domains. Heritabilities were 0.62 (VA), 0.49 (VC), 0.52 (SA), and 0.20 (SC). Genetic influences were due to one common factor with no specific genetic influences. This shared genetic factor also explained almost the entire covariance between the domains, as environmental variance was largely specific to each subtest. The finding of no genetic influences specific to each subtest may be due to the uniquely matched design of the VESPARCH 1, reducing confoundment of different test modalities used in conventional tests. For future research or when interpreting previous studies, our findings highlight the importance of taking such potential artefacts (i.e. different test modalities for different sub-domains) into account when exploring the relationship between cognitive sub-domains.