First appeared in Analog 1977.
I'm a big fan of the novel by the same, Ender's Game (Nebula and Hugo winner, runner up in Locus), which is coming to theaters soon. Once you've read the novel, the story (nominated for a Hugo and Locus, winner of the Ignotus, reprinted multiple times), seems thin, but it still has much to dig in to, philosophically speaking.
Ender opens the tale explaining the nature of his game. One, "the enemy's gate is down." This famous phrase is not just orientation in a "world" (space) where there is no orientation, but also it is a positively framed phrase of confidence. It could as well have been "up" (lack of confidence) or "across" (equality).
Other rules of Ender's game: One, you have to be willing to sacrifice the small things--i.e. legs--in order to win. Two, you can't see disability (frozen legs) as a weakness--rather, find a workaround. Implied as well, just because you're small (Bean) and underestimated and demeaned, doesn't mean you won't have great potential, perhaps even a favored status with your commander, even should he insult you (see "The Pain Problem, 'Fat Farm' and Understanding the Work of Orson ScottCard"). Finally, being good doesn't mean you can't improve: "They were a good group, maybe. They'd get better." As well, he'll give Bean what he wants after he proves himself.
Since the story deals with children playing out adult army situations, Card makes it clear that children are more capable than we think them. Anderson and Graff--adults in charge of the school--argue about allowing children into adult situations. Next these not so gentlemen, after Ender proves himself, give Ender multiple disadvantages through which he pulls through.
When Ender triumphs in the battle room, the game changes. He must battle an enemy whose weaknesses are not known and should not be underestimated (which could be the case if one were overconfident).
The story concludes that the game is not a game: The final games had been real, and no one had told him. Ender had cheated to win, but his win comes at the cost of many lives. In other words, the games we play have consequences for children when they become adults. At some point, more of what the adult "game" should be revealed. In other other words, the above is a good list for guiding youth: Be confident; sacrifice the small for the big; don't accept limitations; take gibes; but don't allow confidence to let your guard down.
As a teacher, I'm constantly thinking about "What do I wish I knew at their age?" Sometimes, I point things out. Sometimes, I'm not sure if we won't make the same mistakes. How many times do we point out that X will be advantageous and students avoid X? How many times, for that matter, do we ourselves fall into the same trap? Still, food for thought.