Heinlein Juveniles

High school students enter a time gate to an unknown planet for a survival test, but something goes wrong and they have to learn to survive by their own resourcefulness. ...

A high school senior wins a space suit in a soap jingle contest, takes a last walk wearing "Oscar" before cashing him in for college tuition, and suddenly finds himself on a space odyssey. ...

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In a futuristic military adventure a recruit goes through the roughest boot camp in the universe and into battle with the Terran Mobile Infantry in what historians would come to call the First Interstellar War ...

Jim Marlow and his strange-looking Martian friend Willis were allowed to travel only so far. But one day Willis unwittingly tuned into a treacherous plot that threatened all the colonists on Mars, and it set Jim off on a terrfying adventure that could save--or destroy--them all! From the Paperback edition. ...