Bioecological theory predicts that cognitive ability is more heritable among those raised in higher socioeconomic status (SES) families. However, the mechanism of this effect is unclear, and the effect may not be universal. We tested for gene × SES interaction effects on Full-scale IQ in 2307 adolescent Australian twins (mean age 16.2 years). Mean IQ scores were modestly higher among those from higher SES backgrounds, but the magnitude of genetic influences on IQ was uniformly high across the range of SES. Research identifying the conditions under which expressed genetic potential can become decoupled from parental SES, as seen here, is needed. We speculate that school provision may be key.