Was the "game" deception necessary for Ender?

The usual line of thinking about "Ender's Game" and the deception of "this is training on simulators" that gave name to the book title is that it was necessary, because the kids could not have handled the knowledge if they knew that the Third Invasion battles were real and not just simulator tests (as evidenced by the answers to this question). That Ender could not have been as able to either send his soldiers to their deaths, OR to destroy the Hive Queens in the last battle, if he knew if it was for real.

However, Ender generally seems incredibly mature for his age, and basically adult like in his thinking. So, it seems to me that if he knew that this was for real, he would still be able to perform his duties.

Do the books somehow address this? I'd like book evidence, not opinions.