A War of Gifts

From the #1 New York Times bestseller
At the Battle School, there is only one course of study: the strategy and tactics of war. Humanity is fighting an alien race, and we fight as one. Students are drawn from all nations, all races, all religions, taken from their families as children. There is no room for cultural differences, no room for religious observances, and there is certainly no room for Santa Claus.
But the young warriors disagree. When Dink Meeker leaves a Sinterklaaus Day gift in another Dutch student's shoe, that quiet act of rebellion becomes the first shot in a war of wills that the staff of the Battle School never bargained for.
Orson Scott Card's novel Ender's Game is the basis of the hit movie of the same name.
THE ENDER UNIVERSE
Ender series
Ender's Game / Speaker for the Dead / Xenocide / Children of the Mind / Ender in Exile / Children of the Fleet
Ender's Shadow series
Ender's Shadow / Shadow of the Hegemon / Shadow Puppets / Shadow of the Giant / Shadows in Flight
The First Formic War (with Aaron Johnston)
Earth Unaware / Earth Afire / Earth Awakens
The Second Formic War (with Aaron Johnston)
The Swarm / The Hive
Ender novellas
A War of Gifts / First Meetings