August is very glad he took a tour of the school, as he's able to find his way to room 301 without ever looking up. He pretends not to notice when kids stare at him. He chooses a desk near the back of the room and watches people's feet as they walk in. Nobody sits next to him, but Charlotte waves. Julian completely ignores August. Jack, however, sits right next to August and greets him warmly. Ms. Petosa waves the last few students into their seats and seems to hesitate for a second as she notices August. She explains that she'll take attendance and then distribute combination locks, and says that the students aren't to try to open them yet.
At this point, August has long hair to protect him both from other people's stares and to give him an excuse to not look at his peers. This shows him trying to hide his identity from others, mostly because he doesn't feel comfortable trusting other kids his age with his real identity. When Jack decides to sit with August, it shows that he's opening himself up to possibly get past August's outward identity to form a real friendship.
When Ms. Petosa gets to a boy named Henry, she notices that he's sitting in a seat with another boy. She tells him to take the empty seat next to August, which Henry does grudgingly. He puts his backpack up on the desk to shield his view from August. Finally, Ms. Petosa calls August's name. He feels his classmates staring at him when he goes up to get his folder and then resists spinning his lock. He watches Henry try and fail to open his lock as Ms. Petosa calls the last few names. She smiles at everyone, and August is somewhat shocked to see that she looks normal and not like a teacher from a movie. Henry is still struggling with his lock, and August confides in the reader that he would've helped Henry if he hadn't put his backpack between them.
August will say on several occasions throughout the novel that a lot of the time, kids aren't actively trying to be mean when they react negatively to him; they're just scared. In the case of Henry, however, this clearly isn't what's going on. The fact that Henry isn't reprimanded for his rude behavior reminds the reader that in a school setting, there simply aren't enough teachers to have eyes on all student interactions at all times—small but hurtful moments like this will inevitably go unnoticed.