In a Heinlein juvenile, a young boy typically (one was a girl) grows to maturity, in the process of living through and effecting events projected into our next century, by means of making decisions that involve his intelligence and mold his character. (p. 144)

[The vision Heinlein gave teenagers] was like Horatio Alger's in some ways, not only because it gave its readers a sense of their own potential, but also because it made clear that this potential could be limited as well as enhanced by scientific, technological, social, and psychological factors. Since Heinlein's juveniles are still popular in libraries, and are never out of print, millions by now must have been introduced by them to the concepts of science fiction, to science fiction as myth, and to science fiction as literature.

It was not until the Sixties, however … that he became a really popular writer for "adult" audiences...