The War of Gifts

If you like the Ender series, you will enjoy this short story by Orson Scott Card. It takes place at the Battle School during Christmas, where all religious observance is forbidden. There is only one purpose, only one curriculum: the strategy and tactics of war. The children are drawn from all nations, all races, all religions, and are expected to leave all their cultural differences on earth. But they are kids. One boy leaves a Sinterklaas Day gift in his best friend's shoe and that quiet act of rebellion becomes the first shot in a war of wills with the staff of the Battle School.

It's only 126 pages, but was an enjoyable holiday read.