The description of Ender's first meal in the Battle School, (as found in Ender's Game) shows them eating their meal at the same time as the rest of the school. Ender even talks to an older kid. (Mick)
He noticed that the older boys were divided into groups, according to the uniforms they wore. Some with different uniforms were talking together, but generally the groups each had thcir own area. Launchies-- their own group, and the two or three next older groups all had plain blue uniforms. But the big kids, the ones that were on teams, they were wearing much more flamboyant clothing. Ender tried to guess which ones went with which name. Scorpion and Spider were easy. So were Flame and Tide.
However in Ender's Shadow, we learn that fresh arivals have their first day on a different schedule then the rest of the school.
It was mealtime, then. They were alone in the mess hall -- as fresh arrivals, they were on a separate schedule that day.
So then why was Ender's launch group eating with everyone else the first meal?