August explains that after his jaw surgery, when his jaw was wired shut, Mom started asking him to rate pain on a scale of one to ten, since he could do that without talking. She continues to ask him to rate things on a scale to this day. After school, August meets her outside and tells her that his day was a five. Mom is surprised, but she tries to carry August's heavy backpack for him. August yanks his backpack away from her and leads her through the crowd. He waves at Summer when she yells goodbye, but he avoids Mom's questions about her.
Mom's surprise and desire to carry August's backpack suggests that she wants to do what she can to keep him safe, even if she can’t be present during the school day. When August rejects her attempts, it shows that he's feeling far more independent than he did only a few weeks before. Then, when he rates his day a five despite Julian's bullying and Henry’s rudeness, it shows that August is relatively optimistic and is willing to focus on the good, like his new friend Summer and his teacher Mr. Browne.
Mom tries to ask other questions about August's day, but August gives cursory answers. He chooses to not tell Mom about Julian's Darth Sidious comment and can't quite figure out why he feels mad at Mom. She asks about Summer again, and August responds that they met at lunch. He says they're like Beauty and the Beast and runs away before Mom can say anything.
August's answers here suggest he may be trying to punish Mom a little bit and make her feel bad for sending him to school, even if school was relatively a good experience. This continues to show that growing up isn't a linear or easy experience; even as August thinks he might enjoy the experience, he can still resent the person making him do it.