Utilizing ECLS-K:2011 data, this study compares adopted and biological children to account for the role of heritable characteristics in explaining the relationship between family environments and children's cognitive skills. I find that cognitive skills do not differ across adopted and biological children after adjusting for the systematic differences between them. I also find that the relationship between family environment and children's cognitive skills does not differ across adopted and biological children. Taken together, these results suggest that the relationship between family environment and children's cognitive skills is not spurious.