Tunnel in the Sky

Tunnel in the Sky is a science fiction book written by Robert Heinlein and published in 1955. It circles around a training mission gone very wrong which strands a group of students on an uninhabited planet for several years, and depicts their hardships, culminating with their eventual return.

Wikipedia contains spoilers

Plot Summary

Rod Walker, a senior at Ponce de Leon High School, was preparing to take his final exam in solo survival. His sister, a captain in the Amazon corps, advised him not to take a gun, pressing him to take her knife "Lady Macbeth". Deacon Matson, impressed equally by the advice and by Rod's acceptance of it, gets the girl's address.

Rod intended to team with Jimmy Thraxton, but he couldn't find him after going through the gate. A long, tedious time of trekking through the wilderness seemed to be ahead of him when a moment's inattention opens him to attack by another student.

Whean he regains consciousness hours later, Rod finds himself stripped of all but his shorts and a bandage-cached knife -- the one his sister lent him. Grimly determined that "someone was going to be sorry", Rod threw his knife to down a baby buck -- but it eluded him. He tracked the buck by its spoor to where he found another student butchering its carcass. He surprised the student, saying, "Cry pax and mean it, and we'll both eat," and threatening to kill his prisoner with a long sharp thorn to the neck otherwise.

The other student surrenders and a brief but wary conversation ensues. Jack Daudet and Rod introduce themselves; it turns out Jack has heard of Rod's teacher: "The Deacon himself!" The two agree to team up (at least temporarily), despite their violent meeting.

Back in Jack's cave, Rod tries to justify his actions but makes things worse when he spots Lady Macbeth being used by Jack to cut roast meat. He grabs Jack's hand and demands the knife. Jack says, "You can make me drop it, but if you do you're breaking up our partnership right now." Rod backs off this time, and Jack tells Rod about getting the knife. Despite being mad at Rod for this second assault, Jack chooses to make up with him, in part because something has gone wrong: their pickup is long overdue. Apparently a supernova is interfering with the gate.

The pair decide to seek out other students (cautiously). They try tracking, but their quarries all manage to elude them until they locate a boy living in a tree whose description reminds Rod uncomfortably of Jimmy Thraxton. Jimmy hasn't come down in over a day, and Rod thinks he may be sick. He goes up and gets him and brings him up to the cave, mindful of the carnivorous fish in the creek below the cave entrance.

When Jimmy regains consciousness, he and Rod are catching up when Jimmy does a double-take. It turns out Rod thought Jack was a boy, but she's really a girl: her full name is "Jacqueline Daudet, want to make something out of it?" The two boys turn their backs while Jackie wriggles out of her body armor.

No point in summarizing the rest of the story; just go read the book!