When Ender first arrives at Battle School, he is one of the launchies, the younger boys who are not yet assigned to armies. Most Battle School boys remain launchies for two years, but Ender is promoted to Salamander Army after just a few months.
From the time of Ender's promotion, he participates in four armies: Salamander, Rat, Phoenix, and Dragon. Salamander Army's commander, Bonzo Madrid, hates Ender and trades him as soon as possible. Ender goes directly to Rat after Salamander, not to any other army in between.
Salamander's commander, Rose the Nose, is not much more interested in Ender than Bonzo was. However, one of Rose's toon leaders, Dink Meeker, sees Ender's promise. Ender gains respect as he rises through the ranks. In Petra Arkanian's Phoenix Army, he becomes a toon leader. Finally, in Dragon Army, Ender is a commander.