This is one of Heinlein's "juvenile" novels centered upon and written for teens. Rod Walker and other teens start out taking a basic survival test, but something goes wrong and they're stranded on a deserted jungle planet. The novel has been described as the inverse of Lord of the Flies and I even saw a recommendation comparing it to Hunger Games. This is a novel about survival, but here the group of young people struggling against nature itself, not each other, and leadership and cooperation is the theme sounded, not a destructive tearing each other to peaces.
I saw some reviews noting how dated the book is in that the boys and girls pair off so neatly and speculated that Heinlein being a product of his times didn't have the imagination to do otherwise. That would be a no. There was even a very early novel written by him in 1938, not published until after his death, For Us, the Living, that included nudism and "free love," both themes he'd take up with a vengeance in books such as Stranger in a Strange Land published in 1961. But Tunnel in the Sky was contracted for a teen market--and in 1955. Suffice to say Heinlein certainly had even back then the imagination to create alternate lifestyles--he just wasn't free to describe such a world here. And ironically, I think his juveniles are the better for it, even if they strike a rather old-fashioned note from time to time.
