The answer to this question can be found in Chapter 11, which records the battle that Dragon Army fought against Rabbit Army and the defeat that Rabbit Army suffered. When Ender and his troops go in to lunch, the narrator reports that the scoreboard that formed such an important part of the endless and taxing games that the children were forced to play has a new commander in top position. The following quote describes who is now the best commander out of everybody:
Ender had the best rankings. A perfect won-lost record, of course, but in the other categories he was far ahead. Average soldiers-disabled, average enemy-disabled, average time-elapsed-before-victory--in every category he was ranked first.
The quote conveys the excellence of Ender in his military achievements, especially considering he has only recently been promoted to commander of his own army. It emphasises his skill and battle knowledge, and also how outstanding he is compared to the other commanders. Of course, as he later comes to realise, this makes him in many ways a target.