In order to fully challenge Ender, Graph and Anderson begin changing some of the most traditional expectations in the game as soon as Ender gets his own army.
First, "Dragon Army" is one that hasn't existed in many years. Instead of taking command of an existing army, Ender is put in charge of a group of kids who are all younger than he is, and most of them are very inexperienced.
Then, because of the elite practice sessions Ender has been holding, there is a new "no trading" rule. Ender will not be able to get rid of any of his soldiers for students who have more experience and more training. He is stuck with exactly what he has.
Then, the battle schedule changes. Instead of a few battles a week with days off in between, Ender's army is challenged seven times in seven days. When they win all of them, he is given two battles in one day. During one of these battles, the rules change to allow frozen soldiers to become unfrozen after a short amount of time (rather than for the duration of the battle as was the case before).
And finally, the teachers give him a battle against two armies.
It seems the odds continue to be stacked against Ender's favor, and yet, he manages to win everything.