"Gulf", and he wasn't a mutant, just on the far right of the bell curve. They were trying to breed a new human race from the extremely intelligent. The techniques used in that story were mostly based on General Semantics, like the Null-A novels, but took it in a different direction.

When I wrote Heinlein's juveniles, I was thinking more of "Rocket Ship Galileo", "Farmer in the Sky", where the protagonist is learning the importance of thinking clearly and accurately.