It's strange to think of your teachers as being people. (4.6.8)
Teachers Are People: News at 11:00. But seriously, this is just another part of growing up: realizing that adults, even teachers, are people, too. Hey, they were even kids once. They might have been through the same things as you and made the same mistakes you made.
All I cared about was the fact that Sam got really hurt. And I guess I realized at that moment that I really did love her. (4.12.32)
This declaration shows a real maturity on Charlie's part. During his relationship with Mary Elizabeth, Charlie hoped to make Sam jealous, but now he's just worried about her. That's assuming that he isn't just writing this to convince himself—but that's another discussion altogether.
"I do consider you a friend, Charlie." (4.12.55)
Bill feels he can talk to Charlie as a peer. What do you think of this relationship? Does Bill assume too much maturity in Charlie, or does he just see his potential?