Why does ender practice with his original launchie group?

After Ender is reassigned to Salamander, his commander, Bonzo, will not let him participate in any battles or practices, being worried that Ender will hurt Salamander's good record.

In the battle room, Ender learns by watching Bonzo and the soldiers. He studies the way Bonzo commands, learning both what to do and what to do differently. He also considers the formation of the toons, the subgroups of soldiers in the army (generally in groups of ten with one leader): the toons are too formal, too rehearsed, while more fluidity would give them an advantage.

That night, Ender goes back to his old Launchie barracks to get his younger friends to practice with him. He teaches them techniques from the armies and practices his new skills.

the longest time is 123 years