"In science-fiction circles," says Willy Ley on the jacket of Robert A. Heinlein's Tunnel in the Sky … "it has become customary to use Robert A. Heinlein as the standard; unfortunately for most writers, that standard is too high." I agree wholeheartedly—with the addendum that the standard is sometimes a smidgin high for the Old Master himself. This story of high school students who are, for a senior seminar in Advanced Survival, translated to an unknown planet to survive on their own resources is, by the Heinlein Standard, a rambling and not compelling tale, particularly weak on character-creation; but its detailed plausibility and careful thinking set it, of course, well above the run of teen-age science fiction.