That is a newly published piece by Elliot M. Tucker-Drob and Timothy C. Bates, the abstract is this:
A core hypothesis in developmental theory predicts that genetic influences on intelligence and academic achievement are suppressed under conditions of socioeconomic privation and more fully realized under conditions of socioeconomic advantage: a Gene × Childhood Socioeconomic Status (SES) interaction. Tests of this hypothesis have produced apparently inconsistent results. We performed a meta-analysis of tests of Gene × SES interaction on intelligence and academic-achievement test scores, allowing for stratification by nation (United States vs. non–United States), and we conducted rigorous tests for publication bias and between-studies heterogeneity. In U.S. studies, we found clear support for moderately sized Gene × SES effects. In studies from Western Europe and Australia, where social policies ensure more uniform access to high-quality education and health care, Gene × SES effects were zero or reversed.
I would put it this way: genes matter more when you equalize environmental influences in the United States, but not in many other countries. By the way, this also holds if you control for race and the greater racial diversity of the United States. One possibility is that there are greater environmental differences to be equalized in America in the first place, compared to say the Netherlands, one country where the gradient is quite different. In any case an interesting piece.
For the pointer I thank Michelle Dawson.