The NLSY is the classic example of this. It was a multi-decade study over thousands of people which looked at a variety of things as the kids aged into adults a

The NLSY is the classic example of this. It was a multi-decade study over thousands of people which looked at a variety of things as the kids aged into adults and through their lives. The wealth and IQ correlation was one of the results, and if you're interested in reading more I'd recommend The Bell Curve by Herrnstein and Murray, who were Harvard professors who primarily followed this study and reported the results in regards to IQ, as well as the other majors studies and their results.