What were the results of Terman’s study? What does this teach us about “geniuses”?

From the text:

When the Termites were into their adulthood, Terman looked at the records of 730 of the men and divided them into three groups. One hundred and fifty the top 20 percent fell into what Terman called the A group. They were the true success stories, the stars, the lawyers and physicians and engineers and academics. Ninety percent of the As graduated from college and among them had earned 98 graduate degrees. The middle 60 percent were the B group, those who were doing “satisfactorily.” The bottom 150 were the Cs, the ones who Terman judged to have done the least with their superior mental ability. They were the postal workers and the struggling bookkeepers and the men lying on their couches at home without any job at all.

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What was the difference between the As and the Cs Terman ran through every conceivable explanation. He looked at their physical and mental health, their “masculinity-femininity scores,” and their hobbies and vocational interests. He compared the ages when they started walking and talking and what their precise IQ scores were in elementary and high school. In the end, only one thing mattered: family background.

The As overwhelmingly came from the middle and the upper class. Their homes were filled with books. Half the fathers of the A group had a college degree or beyond, and this at a time when a university education was a rarity. The Cs, on the other hand, were from the other side of the tracks. Almost a third of them had a parent who had dropped out of school before the eighth grade.