August reads in his cabin until two in the morning. He explains that nobody noticed that he'd even been gone when he got back to the movie screen, and he marvels that nobody knew that something bad almost happened to him. To everyone else, it was an ordinary night, and he thinks that there are probably people who had a fantastic night.
August's recognition that other people in the world had a great evening shows that he's beginning to truly think about other people's experiences and recognize them as just as important as his own, evidence that he's growing up.
Amos, Miles, and Henry told their friends what happened and the story spread, all the way to the teachers. Mr. Tushman talked to Amos, Jack, Henry, and Miles about the boys that tried to attack them, but when he spoke to August, August lied about not remembering Eddie's face. Lying in bed, August thinks that Eddie's face is what he sees every time he tries to close his eyes. He thinks back to Dad's mention of August being “a lamb to the slaughter,” and thinks he finally knows exactly what it means.
As August comes to a deeper and more personal understanding of what "like a lamb to the slaughter" means, it shows that part of growing up is reevaluating things he thought he already knew time and again as he experiences things that change his understanding and perception. It's possible that August will continue to mull over this saying for the rest of his life.