Humans are colonising the galaxy, thanks not to rocket ships capable of taking us to remote star systems, but gateways through hyperspace that allow us to travel anywhere in an instant. But before people are allowed to start a new life in a frontier world, they must take survival classes which culminate in a test in which students are dopped into alien environments and must survive or die.
Our protagonist is takes his test and is sent to an alien world (along with many other students) only to find himself cut off and stranded after something goes wrong. He soon realises that he is better off finding others and living together than remaining on his own although it then becomes apparent the the social problems of living in a group can be trickier than anything else.
While the initial premise of the book is gripping and entertaining, it is what happens when things go wrong and the students are forced to agree their own social structures that things get more interesting and thought provoking. As more and more stragglers turn up the problems of coordinating their efforts to ensure everyone is safe and gets fed become trickier. Eventually they find themselves to having to establish some form of government in order to impose effective disipline; as one character comments: "Government is the art of getting along with people you don't like". And the problem of what to do with unsocialable individuals who just won't tow the line manifests itself too.
This is also a form of coming of age tale for the protagonist as the harsh realities of survival and later responsibility turn him from a youth into a man.
Whilst this is one of the better Heinlein novels I have read, it was still not perfect. Flawed characterisation with often irritating and pointless exchanges permiated the story but then I've come to realise that characters aren't his strongpoint and the story and handling of ideas generally more than made up for this.