The figure above comes from the paper below. A quick glance shows that for pairs of individuals: 1. Increasing genetic similarity implies increasing trait similarity (for traits including height, cognitive ability, years of education) 2. Home environments (raised Together vs Apart; Adoptees) have limited impact on the trait (at least in relatively egalitarian Sweden).
It's all here in one simple figure, but still beyond the grasp of most people struggling to understand how humans and human society work... See also The Mystery of Non-Shared Environment.
Genetics and educational attainment
David Cesarini & Peter M. Visscher
NPJ Science of Learning 2, Article number: 4 (2017)
Abstract: We explore how advances in our understanding of the genetics of complex traits such as educational attainment could constructively be leveraged to advance research on education and learning. We discuss concepts and misconceptions about genetic findings with regard to causes, consequences, and policy. Our main thesis is that educational attainment as a measure that varies between individuals in a population can be subject to exactly the same experimental biological designs as other outcomes, for example, those studied in epidemiology and medical sciences, and the same caveats about interpretation and implication apply.