John Scalzi has an on how relevant Heinlein is to today's young readers.

Somewhat depressing.

Yes and no. Scalzi's daughter Athena is at an age where she's not necessarily going to be enthralled by books that her parents read and recommend. She's in her mid-teens, after all.

The world has changed a lot, too. Some parts of Heinlein probably seem less relevant to the next generations than they did to us, for reasons I mostly like. For example, most of my nephews, nieces and godchildren wouldn't understand how ahead-of-his-times Heinlein was when he portrayed women working professionally, because it would never have occurred to them to question a person's ability to do particular work on as irrelevant a basis as their gender. The views Heinlein expresses about sex in Stranger in a Strange Land and later works, which I found shocking enough that they put me off Heinlein for a few years when I was a teenager, don't shock them or even sound particularly strange. They're still a bit young to understand the deeper stuff -- all the material that shows Heinlein as something other than just a popular writer. Fortunately "still a bit young" means that they'll probably grow into it.

I made a deal with my then early teenage daughter. I read a book she chooses and she reads one I chose. Anyway I read Harry potter and she read star beast. She didn't ask to do the deal again. she is now 19 and only reads manga. Or non fiction, oh and a million text messages and websites.

I think RAH's work will be more likely to endure for his philosophic view point rather than his appeal to adolescents. I tend to suggest his work to psychology, anthropology and ethnology students who respond very well to RAH's exploration of human relationships and how they are likely to evolve under the influence of science replacing superstition in society.

For example:
Social conditioning against breeding with 1st degree relatives is a result of the increased number of defective offspring this produces. The parallel result of the small number of superior offspring this also produces tends to be less visible in terms of the average persons ability to understand statistical outcomes or even perceive the universe around them. The 1 in 4 offspring who exhibit reinforcement of the superior traits of their genotype tend not to hang out (too busy off being successful) with their more defective relatives and therefore the prohibition is further reinforced by social perception of a family group which is known to inbreed.

The Howard foundation is Heinlein's response to this - he even comments on the higher incidence of "defectives" in the early stages of the breeding program. However as the gene pool becomes cleaner through the preservation of the superior phenotypes and elimination of defectives from the breeding group (not killed just not bred back into the genotype). He enables the reader to overcome the EXTREMELY well programmed "screwing your sister is a mortal sin" ethnocentricity of a majority of human societies.

Show this to a University student studying philosophy, genetics, sociology, psychiatry or any related subject and they become almost instantly hooked.

University students (bouncers) are the most common juvenile form of the Academic (Martians) - Academics then mature into Professors (old ones). Professors set the reading lists which University students are exposed too . I tend not to give RAH to teenagers - they haven't learned to think yet, but early twenties when idealism and intellect combine seems to be the best time.