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I’m interested in this question, and I am asking in order to be enlightened by you, dear reader.

Suppose you had twins, separated at birth, Norman (for “normal”) and Gene (for “genius”).  Norman receives an ordinary middle-class upbringing, without much special early learning.  Gene gets the most effective early training that you can imagine, whatever you imagine that looks like.  Next, suppose that Norman, after an ordinary, decent education, has an IQ of 100 (i.e., average).  I’m guessing that Gene would have an IQ slightly higher than 100, and that he would do better and be more motivated in school than Norman.  What I am not convinced of is that it is even in the realm of possibility that Gene will become a certifiable genius, with an  IQ of 140 or higher.  The only circumstance in which Gene has an IQ over 140 is if Norman’s IQ is well over 100.

In other words, while certain kinds of early education can have salutary effects, one of the possible salutary effects is not to give a genius-level IQ to a child who would otherwise not have a genius-level IQ.

Am I wrong?  Can you point me to any discussions, books, or studies on the question?