Verne names Defoe in his own preface. He opens Two Years' Vacation by saying that many Robinsonades have been written, that he has written one himself already, and that what remained to be done was a Robinsonade with children in it and no adults at all. So the book is constructed as an answer to a form it names:
- Castaways on an uninhabited island, with the story made out of the work of surviving there
- Inventory and method as the actual content: shelter, fire, food, mapping, a calendar
- Time measured in years rather than scenes, so competence accumulates
- Rescue as the ending rather than the escape being the plot
Verne's change is the one the preface promises: fifteen schoolboys and nobody in charge, which turns the practical problem into a political one and is why the book is read alongside Lord of the Flies.